Carl has it right. The engine metal tag was intended to be the long term ID for buying replacement parts for the engine. The paper tag was for quick identification on the assembly line. It was understood that paper would not last more than a little while exposed to weather, oil leaks, anti freeze spills etc. The Build sheet, the paper engine tag, and the MPC all have the matching engine codes for each model year / engine size / application clearly differentiated.
Here's the page for the engine tag decode from the Master Parts Catalog. Notice that the only plants identified are Windsor and Cleveland - they never added the Lima plant, and it was assumed that if it was blank it meant Dearborn.
This is what led companies like ECS to make "reproduction" paper tags that are in fact not accurate reproductions of anything because they all have an "L" as the plant code. I made a sheet of them (adhesive backed) with the proper "D" and then used a Scotch packing tape dispenser to cut them as if they came off a huge roll.