Knowing that my data was accurate, I created a breakpoint in the debugger to ensure that the data was being loaded correctly — and it was. At this point I just gave up and went to work on other tasks (like the case of the missing pitch). Sometimes your brain just needs a break.
I came back to the Glavine bug over the weekend and saw the same thing: the data was correct and it was being loaded correctly. Then I clicked 'F4' in Excel and the cursor jumped all the way down to line number 90160 where Tom Glavine was listed a second time — but without the 'L' flagging him as a lefty. With a blank data field, Baseball Mogul was giving Glavine the default throwing hand (righty).
I have no idea how this bad data ended up at the bottom of the "master.csv" file (for Glavine and ~8,200 other players whose last names start with 'G'). I get biograhical data from the Baseball Databank, and I guess I grabbed a file that hadn't been finalized yet.
Anyway, Version 24.13 fixes this bug by removing the bad data (although you will need to start a new game to see the changes). Sorry it took so long.