A simple enough question, hopefully with a simple answer. When was the discussion held (and presumably the decision taken) that questions on SFF:SE should relate to a single canon universe?
When was the discussion held (and presumably the decision taken) that questions on SFF:SE should relate to a single canon universe?
I don't believe that discussion was held prior to this one.
Note that this is completely unrelated to the "too broad" close reason, which is not at all stating that all questions must relate to a single canon universe:
There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.
The decision that questions on this site should relate to a single canon universe seems to have been made by a handful of users who closed questions without discussing it on meta, or without waiting for the ongoing meta discussion to be resolved.
The closest I can find is this discussion about "opinion based", which touches on the subject somewhat.
Note that the arguments that this policy has been enforced for a long time seem to be erroneous. For example, the majority of the items in this discussion were closed within the past 2 years. In fact, 4 out of 7 were closed within the past few months, despite the questions being open for years without objection. 1 other was closed about 2 years ago, again, after the question had been around for 2 years without issue.