Penetration will be percent applied on top of penetration value (ie 100*1.05). Penetration is a pretty strong bulletin (on atguns and tanks, not on MGs or mortars that have barely any to begin with) because it will apply on first shot, unlike things like reload which will only help shots following the first.
Armor is same (percent on top of normal value like 234*1.05 for okw piv), and will also apply to rear armor.
Thanks for clarifying Cruzz!
I'd thought of the fact you may only get one shot with a particular weapon when considering which bulletins to use, and may need to make it count. As I had previously suspected how penetration/armour bulletins were handled was the second case as you confirmed.
However I would still say that penetration bulletins are not that useful for generalist Tanks. Rather AT guns and Tank Destroyers/Panzerjagers are the natural units for penetration bulletins. I believe generalist Tanks would benefit more from reload bulletins, especially when used against infantry and light armour, the only targets I normally engage with generalist tanks.
Naturally armour bulletins are useful for anything with high armour values, and yet I don't favor defensive bulletins such as these over those giving increased killing power. Ultimately, my micro ability is enhanced by offensive bulletins, whereas defensive bulletins only come into play when I make mistakes, something I don't have control over. I might even suggest new players stick with defensive bulletins such as enhanced armour and more experienced players with offensive ones.
I have more illuminating questions about bulletins, but will drip them out over a few days so as not to overwhelm.
Thanks again!
Joseph