Is a transliteration tool enough to grant count as SBCS?

Prompted by this. I'll speak about Dyalog APL here, but this could really apply to any language. Background Dyalog APL has its own SBCS called ⎕AV. For backwards compatibility reasons Dyalog Ltd. is reluctant to change the character set. Lately, six new built-ins have been added to Dyalog APL a...