Just to clarify terminology: The Tappet is inside the Lifter.
Schaeffler Automotive Aftermarket Germany | Products | Hydraulic tappet
Most changes to the tappet would not be visible unless you dismantle the assembly and make almost microscopic comparisons between old and new.Both Porsche and INA changed their Part numbers.Porsche #.....72 is the latest. They are at least $40 each from the dealer.The alleged substitute is $9.At this price, I stopped playing with my tappets and replaced them all.
Once the tappet has jammed in the fully compressed position ,it is difficult to remove it without slight damage to the external surface of the tappet. When the tappet is jammed ,it will be noisy in operation.It won't unjam itself with use. If the tappet develops excessive clearances ,it will seem to function correctly but will be 'soft' when you test.It will also be noisy.When you test an unworn tappet,it is quite firm and compresses slowly-assuming it is completely full of oil..
My speculation is that once the tappet wears and goes 'soft' ,it will jam compressed when driven at high revs.When several jam, you'll get pronounced lifter clatter,not just tapping. Trying to differentiate between that clatter and early stages of crankshaft+connecting rod bearing noise is more than my ears+stethoscope could discern.
If your 'lifter' noise is on cylinder #5 (like mine was ) I would be concerned.I had both bearing wear and some tappet collapse issues simultaneously at 90k miles. The interesting question is -"Why?". The correct answer(s) to that question could save a lot of financial distress in the M96 community.
This is all just speculation -I am not an expert.