I collect based, not so much by dates but by systems. I was an avid gamer from the late 70's to the mid 90's so my collection consists of Atari 2600 up to the 16bit Genesis/SNES/TG-16 era.

That's my cut off "date" so to speak. Even though I did own N64/PS1/PS2/Xbox, etc those systems hold no interest or nostalgic value to me so I choose not to collect for those systems from those time periods, even though there are many great games for those systems. For me, a big part too is the space issue. I don't have the room for multiple systems that I won't play much, if at all.

And as others have said, I collect only games that I actually want to play. I used to be a "buy anything and everything" kind of collector (see any of my pick up videos from the last couple of years for evidence of that) but got overwhelmed with the volume of stuff I had and sold a large portion of it and feel better with a smaller, sleeker and more complete collection from a personal preference standpoint.