When Was The Jotter Barrel Diameter Made Smaller?

[rpparker]

My understanding was that the barrel diameter for jotters was made smaller sometime between 1958 and 1973 - which is why the original jotter refill won't fit into later jotters. I have a pre '73 jotter whose barrel is too narrow to take the original refill.

 

But I just noticed that the Royal wedding jotters, from 1981 because it says so on the barrel, can take the original refill - they have bigger diameter barrels.

 

Did Parker keep changing barrel sizes?