I know I can't answer the bold part, can you? Maybe @Micah Sweet can? They seem to care about the canon of D&D a lot. I don't really get it so I would appreciate some clarification if possible.
I appreciate canon for RPGs.
I got the
1e World of Greyhawk boxed set and used it for my decade+ long campaign starting in 85 or so. Greyhawk stuff was supposed to be compatible and part of a whole so adding on and including more Greyhawk stuff was consistent such as running the
Temple of Elemental Evil in the Greyhawk boxed set setting. 2e advanced the timeline and metaplot and adjusted mechanical stuff for the new rules but was still the same ongoing continuing world with that as the design goal. Same with 3e. They did not create narrative lore contradictions through reimagining stuff and doing it differently. I could keep getting Greyhawk stuff and it was designed to keep working with my ongoing campaign. I used the
2e City of Greyhawk boxed set and the 2e Falcon modules in my ongoing campaign when they came out, for instance.
5e Greyhawk changes up some things through intentionally reimagining them and changing their stories to deliberately break from that ongoing continuity. Prominent NPCs change race, the Baklunish now historically launched their magical apocalypse first against the Suel instead of the reverse, the Bone March is different, etc.
Advancing timelines and metaplot have their own potential issues for usability for existing campaigns through changing things through time advancement and in world plot actions but changing canon takes it further by contradicting what was in the older material directly that ongoing campaigns were based on.
It matters for the other direction too in starting with a new edition and looking to use older materials. Using the
3.0 Living Greyhawk Gazetteer or the 3.0 D&D Gazetteer as your campaign setting you could use any 3e or 2e or 1e Greyhawk material and the lore stuff would all be designed to work together. Contradictions exist but they are generally incidental mistakes, not intentional invalidations of other material. With 5e you have to check for contradictions and fit if you want to use older Greyhawk material. Most things will work together but some are going to be incompatible by design.
For the most part it is minor as implemented so far as there is so little 5e Greyhawk and most of the divergences are small, but it is annoying and the more canon divergences there are the less useful different Greyhawk products are going to be for someone using Greyhawk as their setting.
