Postal Stationery Precancels - Dates Of Use?

I assume these are varieties of postal stationery precancels. Can anyone help date them?

If my catalog search is correct, I'm guessing they are either a U420 or U421, which would date the envelopes to 1916, but not sure when the precanceling took effect.

Any ideas?

Sorry, forgot to post the image:

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I have a couple in my Route 66 collection. I think one is for Pasadena CA and also does not have a date, like many precancels. I'll have to check for more info.
I guess I could've added the image already on file.

I'm sorry I don't have the envolope precancel catalogue & only have part 1 of the Post Card precancels.

Mike W

wt1 . I assume you have found out the answer to your question by now, but in the off chance you haven't, NY was authorized to first use precancelled envelopes on Aug 7, 1923.
The Sec. 562 P.L.& R.usage was authorized in 1932. The catalog numbers of these items is dependent on the watermark, envelope size, envelope dies, etc. Very hard to do from cut sqaures. Hope this answers one or two of your questions.

I have several of them as well and always wondered about them.

These cut squares are from U420d envelopes, which used paper with watermarks 28 through 43.

Watermark 28 was used starting in 1929, and watermark 43 ended with a new paper contract in 1953 (with numerous watermarks/contracts in between).