When changing the manual drivetrain clutch how necessary is changing the flywheel?

I purchased a new clutch kit that recommended changing the flywheel and not to resurface it.  I am replacing an identical clutch kit that the previous owner had a shop install which has failed within 3,000 miles.  Is there a way to determine if the shop had replaced the flywheel and got a faulty clutch kit as opposed to installing it wrong?  Are there any obvious tells once I start to disassemble that would point to an answer?  I hope the shop replaced the flywheel so I won't have to contemplate changing the rear main seal.  Are there any factory stamps on a flywheel that could indicate original equipment?  Is there a specific thickness or tolerance required for the flywheel?  Do the clutches being the same part and not like the original equipment make some kind of difference relative to the flywheel? Thanks in advance for taking the time to respond.