The tables with the numbering of Mabie Todd pens are about the newer English pens. I would be interested in the old, four digit numbers in the US.
It seems to me, that pens with a "size 1" nib have a number starting with 3 and "size 2" with a 4. Otherwise I don't have an idea.
3012 is the plain "pocket pen".
4572 is Cob's pen with clip.
4663 is with 18k clip and two chased bands.
Any idea on how this numbering works? There should be three different sizes of pens according to the ads.