Would't have thought about this as a grey area. But sure, you make a valid point.
Basic On-Topic decisions are not only about age and out-of-production (*1) but a soft membrane tethered also at obscurity and what I would call coolness in lack of a better word.
Plus, and that's maybe most important, intention/purpose of a question.
I would think your question may tick all of these requirement. Beside asking for origins, which always works, it's a software question, which nicely can be tied to older eras. VTAM was introduced ca. 1976 (after being vapourware for some time), so one can nicely ask for 1976 VTAM - or better even for BTAM, which had to solve the same issue, even more direct :))
So go ahead and ask.
In case of IBM mainframes it may be rather relevant to distinguish between
- OS,
- Architecture, and
- Implementation/specific family and model.
In case of mainframes this is often blurred into using one term, but meaning some of the other. For example people like to say z/OS when in fact talking about z/architecture or a specific model as if it would be clear. That isn't. So make sure what exactly you're asking about. AMODE 64 being a nice example. While z/OS supports it native, it's not an OS feature buy a hardware one. The same Hardware can run other software that uses this feature.
Being introduced in ca. 2000 I would think questions about compatibility / complications with AMODE 64 could as well qualify. Kinda like asking about Y2K problems 20 years later :))
On a more general level I could not think of many borderline /360ff questions. Either it's really about modern API (or instruction) and clearly off topic, or more likely something that is around since 40+ years
Now, for the translation part, you may as well look at BTAM, as VTAM is more of an additional abstraction layer, hiding more of the nitty gritty details. In BTAM one can still direct access the translate tables (Macro TRNSLATE) for example RASA/SASA for 3270 ASCII/EBCDIC translation. But you might be surprised how much is stil done 'by hand'.
Thinking of it, a generic question about VTAM and NL handling might be also one that is way to broad for a good answer, as it not only needs to differentiate how a terminal is accessed, but also via what configuration. Translation may happen as late as in the terminal controller or as early as within the mainframe ... that is if needed at all.
*1 - In the end the main reason for this cut off is to redirect todaystoday's questions into SE areas which are more appropriate.