typewriterdatabase.com was my main though when I said "the usual sites", so good to know I'm looking in the right place.

Underwood serial numbers appear to be a bit of a mess, with some models having their own serial ranges while others share with the Olivettis they are based on. All very confusing! 1974 seems like a decent guess based on the Studio 46, and it shares the same mechanism as this 450, so that seems to make some sense.

I picked up a nice Olympia Splendid at the weekend - a 1967 model according to the serial number. The paint is mostly good except for some scuffing on the rear where it's rubbed inside the carrying case. The main downside is that the "Splendid" badge on the ribbon cover is missing, which means I don't know if it's the Splendid 33, 66, or 99.

Looking around the internet I found a few sites saying the differences between the three models was minimal, but nothing actually saying what those minimal differences were.