Partial VIN stamped on the block

It is fairly common.

The stamp 'set' were roller dials in a row so they could be spun to the numbers needed at will.

As the rollers wore, or if one broke, they could replace the bad roller.

If a stamp was deemed bad enough, they could also grab a second stamp set & tray again.

Some interesting sets of various stamps & other examples can be seen at The 1970 Hamtramck Registry "Factory Errors (Pg. 1)" Page