I'm having trouble running a16.4 along with a17. I downloaded a16.4 and copied it to a new folder, then re-downloaded 17.
The only one that runs is the one currently installed by steam, a16.4 won't run in a copied folder, it just asks me to log in to steam again and then says it failed after I do.
Right now I just went ahead and re-did it with just a16.4, but I'd like to have a17 too just to check the dev progress on updates.