I'd hope it would have been replaced, not repaired
the older versions were the one's with the "Stretch" issue...if it's replaced the new one should be fine ^_^
is it a private seller?...or trade? if a trade seller (dealer) you'll have some comeback if they haven't been truthful about it
it may be an idea to get someone to look over it ....RAC vehicle check perhaps? (take off the engine cover etc) to see if the chain looks in good order
...but it would depend on how recently they say it was changed to how easy/difficult it could be to tell just by looking at it?
Sorry I couldn't be more helpful...I'll have a quick look in my haynes manual to see if that'll shed more light on the subject
ETA: I can't seem to see anything that would help you to find out if it's been replaced in the haynes manual....