While I wouldn't pronounce upon who should decide the rules in these cases, or on when 'words' become accepted as such, I would observe that people daring to use new should-we-call-them-words seem far less afraid to challenge arbitrary who-says-they're-rules than their ancestors seemed to be.

Compare the verb spec, where both specced, specked, and spec’(e)d are commonly use, but speced isn't common at all.

The short answer is basic illiteracy and poor education, like when people write candys for candies or HTTP defered for HTTP deferred. The OED is clear that this must be relic, relicked as with picnic, picnicked or havoc, havocked. I have the full reference around here somewhere. This is a mandatory orthographic adjustment. I don't doubt you have found many mis-spellings; I can dig up effectively infinite erroneous renditions of separate and occurrence, too, but that hardly makes them right. They aren't, and neither are the ones you've found.

I'd essentially agree with tchrist, though I think his wording might be a bit too strong. Verbs ending in c are uncommon, and although many do take a k in inflected forms, there are more recent ones that often don't, such as "sync/synced". It doesn't necessarily come naturally to people to add the k, and I don't think one can say that adding a k is an exception-less rule of English orthography. For as rare a word as "reliced", it's hard to say what the standard form is, since it rarely appears in professionally edited published works.

@tchrist That's a very prescriptive view. The descriptive view has to be that putting head pests back onto a guitar is a thing but applying one's tongue again isn't.

@Gilles Wut u cawl “prescriptive”, eye cawl “normative education”. Belief it or knot, English spelling duz has rules, not rools or rhouls. It doesn't mattre how meny peeple donut understand how to spell sumthun, that dozen meen they are write.

@tchrist I don't understand your point about "mis-spelling". There's an activity called "guitar relicing" (from verb relic), I did try to google "guitar relicking" and only found one single occurrence, all google hits direct to that one single entry. My 1994 CD Rom edition of the OED is too old to have the word, it only has relicked or relicking as derived from "lick". Could you please cite examples of your probably more recent edition to illustrate the use of "relicking" applied to the activity that consists in making a new guitar look old.

@Laure My point is simple: people do not understand how to spell properly and so make errors borne of ignorance of the actual rule about how these things must be done in English.

@tchrist But when absolutely everybody spells a word the same way even (all the more so ?) when it is a specific word restricted to a technical field why say everybody is in the wrong and you are in the right? Unlike French English does not have an official body that will say what should and shouldn’t be said or written. Besides, being able to make the etymological difference between "relick", to "re-lick" (i.e. "lick again") and "relic", to transform to make look like vintage, can be a help for some - because there's absolutely no common root.

The verbing of this word leads to the unfortunate choice between licking again, or re-adding lice.

Digital - this is exactly what Gilles said in his post and comments 2 hours ago

There's doubtless a 'rule' spelling out how to construct the -ing forms of the verbs focus and parallel, but it doesn't seem to guarantee single acceptable answers. // Wiktionary gives the form musicing, as the gerund (and hence an -ing form), as I read it.

Here's another example of the -cing spelling from AHDEL (though not arising from a final syllable such as -lic or -sic): disk (also disc) tr.v. disked, disking, disks also disced or discing or discs 1. To work (soil) with a disk harrow. 2. To make (a recording) on a phonograph record.

@Laure First, a rule is a rule, even if I were to grant you your condition. But your condition is demonstrably false, and I have demonstrated this in my answer: it is clear that people writing in some curated sources do indeed use the correct spellings. Just because some people don’t know how to spell English means nothing: 240k people spelling it picnicing can and indeed are still wrong. See also seperate, occurance, and all the rest: those are intensely “popular” — and also intensely wrong.

@tchrist Going by Google hits, picnicking wins to picnicing by a roughly 10:1 ratio. Thus picnicking is not only the prescriptively correct spelling but also the descriptively correct spelling. There is no such alignment for relic(k)ing.

@Gilles So your premise is that spelling is a popularity contest? Pretty sure that’s not true.

@tchrist My question is from the perspective of descriptive linguistics, which studies what people says and avoids taking position on what is right. “Popularity contest” is a caricatural way of describing that. I'm asking about the next stage: not the numbers, but a qualitative study of that spelling.

@Gilles So you only want to know why some people fail to observe the -ck- rule? That’s hard to answer.

@Gilles note that spelling is entirely rule-based, people explicitly chose to spell things a certain way (as opposed to spoken language which is error-prone mimicry). Also note that descriptivism even if applied to spelling, is not making a value judgement, just describing. Calling the act of 'not spelling the dictionary way' wrong is a well-accepted value judgement.

@Mitch Sure, but that only applies once there is a rule. This question is about a word that isn't in dictionaries yet. English doesn't have rigid spelling rules like, say, German: it has many words that are spelled this way just because someone chose this particular sequence of vowels to represent this particular regional pronunciation at this particular time. If I was compiling a dictionary and wanted to include the verb relic with its guitar-related meaning, which spelling should I mention?

@Gilles The OED seems to think that there already is a rule. Some of their citations do not follow it: see the verb mosaic, which has published example of both the regular mosaicked and the spurious mosaiced, because there is individual variation and people make mistakes. They are describing what people have written. But they do not consider mosaic an irregular verb, and therefore the established rule applies regularly. Why don’t you just mail them about this? They usually answer honest inquiries about lexicography.

The OED's preference for using -ck- in inflected forms appears to be a part of their house style, not part of their lexicographical information. The Oxford University Press also consistently uses the spelling -ize rather than -ise, but this does not make the -ise spelling a "mistake". There's a difference between the specific spelling rules that the Oxford University Press prefers to follow, and the spelling rules that all reputable publishers/editors will use. How do you know that this rule isn't one of the areas of variation?

@sumelic I guess you meant to reply to tchrist?

That's right, sorry for any confusion.

@Gilles If he would kindly see the full C entry in the OED, he would see that he is mistaken: that this indeed is part of their lexicographical information rather than merely the house publishing preference of -ize over -ise, both of which are “right” spellings. This -ck- rule is really very different from that; I hoped my existing excerpts were enough to show that.