Records made at the Columbia Santa Maria plant can be identified by a couple deadwax features: 1. Handwritten sub stamper codes in the deadwax. These will be separate from the matrix numbers, and usually are a capital letter followed by a number. A4, B13, D1, for example. Based on some research by people on this forum, the best guess is that the letter refers to the mother, and the number is the stamper. 2. Santa Maria pressings typically feature a faint, small handwritten "s" in the deadwax. The "s" is usually on both sides, but I have a fair number of records with the "s" only on one side. The "s" may also be backwards. At the time Santa Maria was making records, Columbia also had two other big pressing plants in operation. Here's how to distinguish records made by them: The Pitman, New Jersey plant pressings have a small stamped letter "P" in the deadwax, and have machine stamped substamper codes. Columbia Terre Haute, Indiana pressings have a fairly large letter "T" in the deadwax, usually etched, but sometimes stamped. If there are sub stamper codes at all in the deadwax, they are typically stamped. Hope this helps. P.S. Forum member @W.B. has noted label font differences between the various Columbia pressing plants. I'm not familiar with the details, though.