Thanks for the info, jorgesurcl! I now have three of such sheets and am trying to link the stamps to the sheets, but am not getting very far.

The Bello engraving is easy, as it goes with the similar 1946 set. The seller dated this as a 1964 sheet, but if you say that those Memoria books only deal with the ten years before publication, then that seems odd. Would you know when this sheet was published? Luckily, the engraving is signed
by Moreno so that's easy.
My second sheet is the Cardinal Caro engraving, which goes well with the 1967 set engraved
by Moreno.

Again, the date of the stamps (1967) does not correspond with the date of the sheet (said to be 1964), so the same question applies here: do you know from which year this sheet is? This sheet is not signed
by Moreno but as the stamps are his, may I presume that this engraving, too, is
by Moreno? And if not, do you know who
did engrave it?
My third and final sheet is the one with the six stamps on, again said to be from 1964.

I'm doing alright with the bottom three: Isabella from 1952, Araucana from 1972 and Domeyko from 1954, all engraved
by Moreno. The dates once again question the date of the sheet, though.
I know the top left stamp is from 1959 but my SG catalogue does not mention its
engraver. Was it Moreno?
The centre stamp, too, is in the SG catalogues (1960/1), but again no
engraver mentioned. Moreno?
The top right stamp I can't seem to find at all. Is that an issued stamp or maybe just an unadopted essay? Is it
by Moreno?
Sorry I have so many questions, but you're so knowledgeable, jorgesurcl, so I hope you don't mind me asking them!