When Don checked material against canon - he checked against GT as well. Only when GT disagreed with other sources was it an issue. If Only GT mentioned X, it's canon. If anything else disagreed with the GT version...
And Don's hermeneutic has issues with clear "Head up WHERE?" moments, like the AHL having Transverse Decks in Mongoose 2E HG... and then claims it was a retcon from the "original intent", when Marc's hand drawn clearly indicates otherwise...
In many ways, it's easier to think of Traveller as a bunch of different timelines all of which share some common features, rather than one cohesive timeline.
You go all over the place with that --- there's so much good discussion material in that post.
Madness to Don's Method
Don was ruthlessly methodically boringly tedious with his order and method thing. Obsessed, he was. This is where he became a true pain in the ass. He really was the best sort of personality for things like timelines and Canon Law. Maksim meanwhile is an excellent Collator, exhibiting some of that ruthless attention to detail that drives me nuts. Thank goodness there are people like that.
Don was adamant about giving publications the benefit of the doubt, because "we're all in the same boat" and any source can enrich Traveller. Of course that sounds like a terribly slow boring way to do things, but that's because I'm not details-oriented.
Don Ran the Nuthouse
Marc would unintentionally drive Don nuts by making sweeping statements about changing something, or doing something in a way that was not particularly tedious enough for Don. For example, not using formula to determine orbits drove Don mad. Instead, Marc did it really rather carelessly. And that sort of thing drives Don nuts. It would have been hilarious if it didn't truly grieve Don's heart.
I, on the other hand, would say things just to see Don explode. But he was too cool a cucumber to explode. He'd get all haughty and dismissive in his actuarial way, and turn the tables on me. He knew I didn't have any real pull to make stupid things happen. But he didn't want Marc getting any crazy ideas, either. Can't have the old man signing blank checks to infidel con artists, after all.
Unnecessary Redundancy
Don was more valuable to Marc than I am. Don's advice was spot-on about timings, announcements, ERRATA, editing, organization, planning, not to mention the Timeline. I am more of an ideas guy, and unfortunately Marc is as well, and his ideas produced this little game that spawned a small company and a career and stuff, so I'm sort of running the Department of Redundancy Department. Marc likes to bounce ideas off of me, but my critiques come from ideas, not practicalities. Don was Practical plus Thorough. His thoroughness made him slow but accurate, and his practicality made him even more valuable.
Traveller IS Parallel Timelines
Finally, Traveller is surely a set of parallel timelines -- the Lorenverse makes that plain. Heck, we could think of eras as modules, nearly as swappable as the rules mechanics. Don't like Book 2? Lots of options. Don't like Virus? Lots of options. Build your own timeline from all the options granted, or roll your own replacement...