The Nightmare Before Christmas Jack & Sally Replacement faces

 

Unpainted Jack and Sally Stopmotion Replacement faces

Auction here

The Nightmare before Christmas used the method of replacement animation for Jack and Sally's speech and expressions. Several hundred, if not thousand replacement faces were cast in resin for the production. Several of these faces where never finished after being casted. That is the claim for these two particular castings. I however, have my doubts. The resin color looks too new to have been casted 30 or so years ago.  For example:

 Here is a photo from propstore.com

of original, unused replacement faces and the color in the resin is obviously different. This is due to the age of the resin. In addition to the color of the resin, there are no markings on the back of Sally's face. Even the unused faces above, show that each face was still marked. 

All that to say, I believe the replacement faces in the auction are re-cast replicas (molds made off originals to create replicas), and not production made. At best, they are casts made from production molds, but done sometime after the movie was completed.