Regarding enchantability, the only thing I can find is the material difficulty table, which I believe is referenced elsewhere across the wiki:
https://gswiki.play.net/Material
However, whether or not that is GM supported, or old data based on changes, it's absolutely ambiguous.
The only thing I can think of from a QC perspective is that it could have been an omission in the materials table. Imagine having a list of materials like that and then asking someone to confirm, but ohh, one line was missing... What should have been caught would be a novalue command in the lookup to bring in a restriction rather than a 0. But, that's 100% speculation based things I've seen on the job.
I agree with Parkbandit on this one. This doesn't appear to be the whole story... Based on the GM posting, it appears that there were more conditions that are a little weird:
1) Knowledge that the enchanting should have been impossible (This seems to be where a lot of debate is)
2) Not discussing whether the enchanting is possible with GMs, or the bug not being properly reported. (This is also the current area of debate, considering your interpretation of 1)
3) Interfacing with people to capitalize on the enchanting
4) Profiting off of #3
As far as Nuadhja's comments... Yeah, there's about a 100% guarantee that there are GMs in HotA, but they can't say who they are... we used to speculate. But, knowing how much Simu got shit in the past for utilizing LNET and Discord conversation in the past, they'd be super shitty and dumb to utilize that in issuance of a warning.