I assumed it was an older word because of the loss of productive 連声 in Modern Japanese. I suppose it must have been formed by analogy? Or, well, I suppose I'm not really sure.
I think just because a dictionary of grammar can be helpful sometimes, doesn't mean they're some kind of bible that should always be followed.
I've actually got a grammar dictionary in Japanese, but it's recommendations are really prescriptive (a lot of sentences I would say are acceptable they say aren't), and a lot of the sentences are just plain stilted, even if technically correct. In addition, there's just no way any grammar of dictionary can cover every way language is actually used in the real world.
日本語文型辞典/the dictionary of Japanese grammar series etc might be useful as a guide, but I don't think they're a substitute for observing the way people actually use the language on a daily basis.
</rant over> :P
(I mean I have an English grammar dictionary written in Japanese)