Calstamp and Pascoe, I would have to agree that they are probably privately printed. But the question is for what purpose if any?
If they were from some type of promotion or from some company, it seems they would have been seen before.
After getting a list of states in alphabetical order, and seeing which states I have. It certainly appears these would have been printed in as sheet of the 50 states.
Below is a scan of all 30 stamps I have, in the positions they would be in the sheet. I also cropped an image from an excel spreadsheet showing the states I have in yellow and the missing states in white. You can see the straight edges are a perfect match.
Another thing of note is these are an odd perf 12-1/2, not sure if that makes any difference at all.
Thanks for any comments,