I don't have those formulas either but you can make educated guesses with some mathematics quite easily. I'm happy to learn you got inspired, always nice to see fellow rohan players enjoy the game!

As for pvp/pve/dd it's in different layers, each having less effect on the initial damage. beside that it looks like some stats have a linear correlation with their counter stat. to clearify this:

say you have 2 players which both have a weapon with 50% damage drop and they are lvl 115. If those players would use 20% pen dd on guarder and 30% wep pen dd they would have 50% penetrate damage drop. In the scenario of them fighting each other one could argue 2 basic scenarios

option 1: having 50% pen dd whilst your opponent has 50% damage drop would result in 50% taken from 50% so the players damage drop gets reduced to 25% DD because of the 50% pen dd

option 2: having 50% pen dd whilst your opponent has 50% damage drop would result in 50% linearry deducted from 50% so the players damage drop gets reduced to 0% DD because of the 50% pen dd.

It seems to me that scenario 2 is the most likely scenario if i see how my damage scales with utilising DD pen stones. I have not tested this but I would assume it goes the same for PVP attack % defense.

As for PVE it's difficult to assess specific scenarios. PVE targets do not simply have pve defense/physical defense/magical defense. Their damage drop conversion works differently. The best stat by far is PVE attack which just percentage wise boosts your final damage with x % but how things like pen defense etc work for PVE, i have not yet figured out.