You can fire hundred rounds into an armoured surface and not be able to inflict damage, if the angle is wrong. The impact of AP hits are not cumulative.
However, there are cases where you fire many shots into an enemy tank and they do not bounce. Apparently the enemy tank did not receive any damage. A friendly tank comes in from another angle, and blows him up with one shot - but you get the kill.
In this case, I can only presume that the shells fired did not penetrate, but did not bounce either. Since it didn't do any damage, the shells probably lodged itself in the middle of the armoured plate. The enemy tank is fine.
However, when the 'determine who killed it' code comes to work upon the target's destruction, these 'lodged' shots will count as 'damage points' to the person who fired at it, and thus, the code will determine that the guy who did not do any damage, but hammered in more AP rounds which failed to penetrate, as the winner, instead of the guy who fired a single round and penetrated, thus, killed the target.
It's probably a flaw of the coding that awards kills, rather than a flaw in the armour model. As of yet, when it comes down to tank vs tank battles, I've never, ever seen or experienced anything inexplicable. (except possibly the undamaged sprockets or stuff as some might pointout - which probably comes from the fact that the tank DM isn't as detailed as plane DM)
As for the AP shots bouncing off unarmoured targets(not puncturing, but actually bounding) - well, got no explanation for that one. Maybe the modelling for light GVs aren't as complex as tanks, and some discrepancy between the two models cause wierd happenings. Most experienced tankers recommend HE shots to kill M-16s or LVTs, instead of AP shots.
Other than that, tank vs tank, anything can happen. And just because it is unexpected doesn't immediately mean its wrong.
