'Old' and 'new' shape DE blades

[NotTheStig]

I know Gillette changed the shape of their double edge blades from the more rectangular shape with just 3 circular holes to the shape we all know now.
I think I saw a vintage ad explaining the new blades but can't remember what it said about compatibility.
Can new style blades be used in the old razors, and can old style blades be used in razors produced right up to this day?
Cheers

 

[hunnymonster]

The 3-hole blades can only be used in the older razors (with 3 pegs to locate the blade) the current pattern blades are universal (but some say too thin for the Gillette Old)

 

[NotTheStig]

Thanks. That's the best way round I reckon, so happy with that