Actually, that's not true. At least in respects to 1675 (not 6542). I can agree that it appears to generally be true. But with all things Rolex, nothing remains today or in the past, entirely true.
Here's circa '60 Pointed Guard 1675 with 1565 and original to the watch Jubilee:
And here's circa '66 1675 with 1575 with original Jubilee:
For 1960s 1675, Jubilee remained somewhat more common in North/South America and Asia whereas Europe tended to have more Oysters.
And there was good reason as to why many preferred the Jubilee.
The 1st generation 20mm Rivit Oyster was the dreaded stretch version which was an INSANE hair puller.
Anyhow, Juan Trippe requested that the PanAm watches be fitted with Jubilee due to the trouble with the stretch Oyster, and later due to the non-stretch Rivit stretching badly only after wearing one for 1 year. The public followed their beloved Boeing pilots and requested Jubilees. Interstingly, the GMT-I was the only sports model to sport (for lack of a better word) a Jubilee.