Unfortunately this is not known, the customer bought the car with the issue and only found out about the head work once the original garage asked him to go back through his paperwork where he found "cylinder valve damage"

Apparently no more info than this I'm afraid?? This is what had us thinking timing.
I checked the physical timing today using the top mark and the lower mark on the timing belt cover and the auxiliary drive belt pulley which shows it's possibly a tooth out? How accurate is that lower mark though? Don't want to needlessly pull it apart? And would a timing issue not be constant??

Thanks for the replies