I'm sorry you choose to be incorrect.

Actually, StormX is right. I asked back when Hair10 was RA, and he did specifically state that it meant you could Perplex AV up 5 times, then do a Transporter MAM and have a +3 net. It was a similar debate to this.
I've also seen Norm confirm this on a post or two on WK. I would give you a link, but I can't access it from work

*comes back from his corner*

Here is one by Nbperp (second post), confirming that StormX and Burleigh2 are indeed right.

*realizes that he changed sides TWO times in this thread, understands that he can't struggle against his Frenchness, goes back in his corner, cursing himself*

Thanks for the followup!

"You must spread some Reputation around before giving it to Drunky again"

Originally Posted by LoSH Rulebook
Many modifiers can affect combat values during the game. Because all modifiers are
cumulative, a special rule called the Rule of 3 limits how much a combat value can be
modified. The Rule of 3 states that no combat value can be modified by more than 3. For
example, if the combat value is 3, it can’t be modified to more than 6 or less than 0.

OK, just to clarify for my sake then. All modifiers are indeed cumulative and only the final result is subject to being truncated by +/-3, yes?

Yes. The end result will be no more than 3 from the printed value... or 3 from the replaced value if they happen at the same time (eg ES/D and Hindering bonus on a replacement DV... no other game effect can increase that DV because of Ro3)

Correct. Just be sure to remember that a "Replacement value" like Defenders TA or BatEnemy TA is not subject to the rule of 3 because they are not modifiers.

Tarnish

So just to make sure we're clear on this, If I used someone increased their defense with ICwO or hindering terrain then 2 Psycho Pirates would give the full -4?

Yes.

Example:
15DV+1 For Oracle+1 for hindering -2 for PP -2 for PP =13 DV

Now if you had a 3 PP doing the same, part of his -2 would be wasted since 12 DV is as low as you can go.

Tarnish

At the point in the action where values are checked is when the Rule of Three come into effect.

So just remember that, "When you Check Values, Check for Rule of Three"

Checking values most often occurs after an Action has been announced, and before the roll.

Well, you can check the values whenever you'd like to... it's just basic math to figure it out. If you forget to check until after the action has been declaired and started, you're out of luck.
Just look before you declair to make sure it's valid. 15 DV +2 for ES/D = 17... it's that easy.
You can figure out how much it would be before the action is declaired.