The Champion 501 is a product of the post-war English wing of Waterman, by which I mean very nearly if not actually post 1940s. The latest reference I have access to for Waterman’s UK factory is a 1947 catalogue, in which the model names and shapes are mostly consistent with those in the same year’s US catalogue, but which shows one unexpected numbered model. The similarity of profile of this pen to the “New Look” pens Waterman-JiF offered in 1948 is quite marked, but the same could be said of the post-war Swan models, too, and I think it indicates a fragmentation of Watermans as its American parent’s doom approached.
Because of the paucity of information I’ve been able to lay hands on, I don’t know if the model number has any real meaning in the same way it did in the old days, or if it’s a mere reference number. I suspect the latter, as it seems to be something the US side was getting up to just before the Second World War. I notice that this pen’s lever is of a very generic sort, rather than of the more complex Waterman lever-box type; whether this argues for lateness of manufacture or mere lowness in the model hierarchy at the time is an open question.
Production Run: c. 1948 – c. 1955 (extremely speculative)
Cost When New: An ad for 1953 shows it at 19s. 3d. (about $2.75; for modern value, try this calculator).
Size: 13.3 cm long capped, 16.4 cm posted, 11.7 cm uncapped.
Point: 14k gold.
Filler: Lever, capacity approx. 0.8 ml.
If you are relying on the preceding information to win a bet or impress a teacher, you should read the site’s scholarly caveat. Remember, this is the internet, and it’s full of bad information.