Just a SWAG, the cast info is more likely the core info, and core level along with the foundry ID and of course the part number.

The numbers stamped in the pad are likely the machined date.

Something as small as a production run like this manifold probably used batches of cast manifolds stored, then when machined had the date of machining as the control.

You will have to look at a few manifolds to see if there is a pattern in the stamping numbers.