Thanks for the advice.
Debt 1 is definately enforceable, compared my copy against the CCA received.
Debt 2 may not be enforceable as the terms do not match the agreement (different document reference codes), but I don't want to have to go through another six years of battle with them (have personal reasons for this). Will check with Clearscore and begin PPI claim.
Debt 3 has unclaimed PPI but as it's statute barred, would any monies claimed go to offset SB debt? I assume so, and if so, it'll be a waste of my time.