In Paul Heaver's 2015 winning squad why does his stress tokens build up as surely he is handing one of these to the defender each time and both players would take control of each others ships next round. I'm confused.

I'm not sure what the question is here.

What do you mean "take control of each others ships"?

R3-A2 simply says that you may receive a stress token upon declaration of an attack to give the defending ship a stress token. A ship can have an infinite number of stress tokens on it so as long as you have targets you can repeatedly trigger R3-A2.

I think you have several misunderstandings here:

1: R3A2 activates when the ship he's on targets another ship (which happens once with the primary and a second time with the TLT, which tagrets only once for both shots). He gives a stress to the defender AND a stress to himself. So he builds up just as much stress as the defender.

2: the only time you hand control of your ship to your opponent due to stress is when you set a RED manoeuvre. All other manoeuvres are fine, regardless of how much stress you have.

So the stresshog just never does red moves.