And re-read your question...
I didn't have any feeling like it was bottomed out, as the bolt barely entered before I could feel the different threads not matching. Once I did get the correct metric bolt, it also did not feel like it bottomed and is plenty tight.
Maybe the previous owner had already run through the bottoming, as my bags are hand made leather by the previous owner, and he had several different amounts of spacers, washers, etc., plus the mounts for a pro-tac backrest, to keep the bolts from extending too far inside the fender...

Mike "Dodis"