Well, I can dismiss one possibility...
I had a duplicate car from the K-Line 20th Century aluminum sets. I came across a complete set of Champ Decals, Blue Ribbon Series, BRO-34, New York Central 20th Century Streamlined Passenger cars. So I selected one car name from that complete set and retained all the others. NONE of them are Atlantic Shore or Rip Van Winkle Bridge.
Besides, they're silver/aluminum in coloration. Your cars appear to be in white lettering.
I tend to think you've got something very special. If you cannot tell that the car name lettering was applied by any secondary means...e.g. water slide, dry transfer...or has any slight difference in any clear coat patina from your 20-6616 set, I'd say it's your lucky day!!
It is interesting to consider, however, that in the Premier (20-) line of freight cars they have been generally released under the same stock number in pairs with each having a unique car number (usually identified on the label as such.) But I can't recall any such paired release in the Premier passenger car lines.
Since most of the MTH personnel who might respond to this conundrum are still around, it might be worthwhile to repeat this inquiry in the MTH forum section....or ask/call/email Midge.
Another possibility...and I'm going far out on a limb here...comes from a search of recent Ebay auctions, wherein I found a 'sold' auction for this pair of cars having your car names under the 20-6616 stock number. (Perhaps it was the auction you won?) Perhaps you could inquire of the seller how they came into possession of these cars, whether they might obtain a confidential clue/answer to your question. In this case, the particular seller is very, very well known, a huge purveyor of collections of this sort. I would bet that their records might have an address, phone number, email address, etc. of the person consigning this item to them for sale. Just a thought.
Keep us posted. This is really a more contemporary 'Who Dunnit?' than most.
KD
