French plastic blanks SFM or

I have following 30-06 boxes for the M1956 plastic blanks in my collection.
It seems that all cartridges/boxes are made by SFM, but why has the box
from 1959 a completely different lot number ( LU instead of SFM) as the
1958 and 1961 boxes ? Where these made by sombody else using SFM parts ?


i hope ,i’m not wrong :the “LU” stand for “” manufacturer