He fudged a little so the Seven Hour War and Combine invasion didn't come immediately after HL1 but a few years later, allowing for mods like Redemption and Poke646 to happen in a world where the inital Xen invasion was taken care of and life returned to normal for awhile. I saw a very rough HL mod timeline on ModDB once which tried to put as many SP HL mods as possible into and around the canon HL games. Specifically I was curious about the timing of the Seven Hour War.
But, I like to wonder how things might tie together into one continuity. The Portal 2 workshop made the infinite multiverse HL canon, which kinda accounts for every fan mod and discrepancy you could imagine. Blue Shift Barney being the one you pass on the tram at the start of HL1. That being said, I love stuff like HL: Alyx explaining Alyx's gun and the toxic gloop all around City 17 in HL2, or Dr Magnussen being the guy whose lunch you ruined at the start of HL1.
The continuity of the HL universe is a hodgepodge of retcons and revisions as all long running franchises are.
