PT-76
Various sources tell the PT-76 is not 12.7mm-proof at the flanks, yet it's rated "2", and therefore 12.7mm-proof, in the game.
"Hard facts" are hard to come by, but
http://www.enemyforces.com/tanks/pt76.htm says
"Frontal armor is inclined in 80.5 degrees. It's upper armor is 10 mm thin while the lower plate is 13 mm thin. Turret has a shape of truncated cone is welded from 10 - 20 mm armor steel.".
Judging from all those pics floating on the 'net, I would say this is correct - surely the armor is nowhere near 20mm, and it's pretty 'boxed', too.