And as far as dating these goes, it is hard.
All of the serial numbers that I could make out in the catalog photos start with 1 and end in 2. The second digits are 5, 6,7, & 8. The serial numbers are 5 digits.
1536x
16542
1798x
18162
With the truss rod covers. I would assume they were made before 1976.
Heck of a coincidence that the last digits are 2. Same with my DT22. Wish I could see more of the serial numbers.
Could these be from 1971 for a 1972 catalog, or more likely 1972 for a 1973 catalog?