My spreadsheet has been a work in progress for almost 3 years now. I'm going for anything: homebrew, hack, port, WIP, demo, etc. I have used Wiki, AA forums, atari2600homebrew.com, along with dozens of other sites too to compile my list.
I have symbols to designate the games on a cart vs. the games made in ROM only too.
The dates I add are mainly just the year. If a game is over several years, I put the whole span of years.
Thanks for any info you can send me AtariCharles!