The 1st bolt was long and fat,,,
the 2nd "improved" bolt was long with a bolt head and a skinney neck( not available/superceeded),,,
The 3rd is a short (no neck)bolt.
The improvements was possibly a harder grade bolt(although there is no indication of this) but most likely is just the increased torque.
I'd replace your bolt and washer on next TB job. They are too cheap not to replace and be sure.

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.