Here’s a couple of 20 x 110RB Oerlikon “S” rounds loaded at the Pirotecnia Militar de Sevilla.
The left one is a conventional HE-T with a brass rotor impact fuze.
The right one seems to be a “modernized” version. It has a streamlined projectile with a longer rotor impact fuze in aluminum. Also it has a wider copper driving band.
The projectile on the left was made at the Fábrica Nacional de Toledo, as denoted by the FNT stamping.
I have no more information on the subject of this “modernized” round, but I think it must date from the 1960’s. Of course much later than the date on the headstamp indicates. Surely they used remaining cases from earlier production lots. The older projectile headstamp is dated 1945 while the more modern one is headstamped 1943.