Permit-imprinted mail is made in huge quantities, but the retention rate is very small. Many have only text instead of a pseudo stamp.
Here are some with with the "Sec 34.66 PL&R" imprint:
Some with the "Sec 562 PL&R" imprint:
Some with the "bulk rate" imprint:
One with a "pre-sorted first class" imprint:
Wood printing block with metal printing surface attached:
Scan of the surface:
Reverse image to be readable: