In my experience with casting design and manufacture, it is unlikely that multiple castings were made at the same time. Some new old stock might have been used after a new one was introduced to foundary production, however. When casting changes are made, the tooling gets modified making it very difficult to go back to the older configuration. On occasion, an insert in the tool can be used to allow multiple design configurations, but this is costly, lowers precision and opens the door to parts with the wrong features. Looking at these blocks, I can see no evidence of inserts being used.