Armour penetration ratings

[Weasel]

How accurate, or how much faith, should I put in the armour penetration ratings you see when you pull up the unit information screen? Reason I ask is I have seen many cases where the data states my gun has enough power to penetrate, yet the round bounces off.

My most notable was a valentine ambushing a tiger from the flank at 80m. Well first he missed with his first 3 shots and when he finally hit the shell bounced. According to data he can penetrate 104mm of armour at 100m and the side of the tiger is 80mm. And my firefly, at 106m bounced a round off the front of a tiger too, and the 17lbr should easily clobber that sucker at that range.

So are the numbers out to lunch? I am really getting frustrated with CM in this regards.