Why not send the sales manager at Stern a direct question for a direct answer on the playfield printing question etc. or the production manager at Stern. Its their job to answer stuff like this honestly I would say.
Even so, I am sure Stern have a great n proven quality method to it. I have Sega Showcase games (also Stern really) and none have any wear at all anywhere on the playfield and they are 1996 to 1998 models etc etc. I cant see anything wrong with any Stern playfields anywhere, and have never heard of any playfield design faults either. Some people have said the clearcoat is too thin, but i am not a believer of that either.
Show me a Stern in the wild with playfield wear for a looked after game. I have never heard or seen one yet that has clearcoat worn away.
Contacting Stern directly via a email I would think would be the best factual way to find out. I will certainly ask 5 million questions when I do the Stern factory tour later this year. That will be alot of fun and a good education i would have thought. Some people travel to Mecca, some head for the Stern tour. I think the later will be more of a religious experience for me.lol