There does seem to have been a series that ran 222, 224, and 226 so yours could well be right. Osmia seem pretty well ordered with their numbers (as far as I can tell, the final number should always relate to nib size). All the more reason for mine to be an outlier. Fabulous nib on the 1222, I bet the 226 is lovely too!
Sorry, I meant to reply to this earlier but wanted to make photos first. No chance, just too busy. So, I'll show pictures later.
Osmias numbering system was kind of systematic but with limitations. I knew only about two- and three-digit numbers and the 22x series was produced in the 1930s as a series of coloured celluloid button fillers. Throughout the years, the last digit indicated some sort of size but probably it wasn't necessarily the nib size number. E.g., I have several 74 models which have #3 nibs, but they were replacements obviously. My 34G has a #3 nib but I'm not sure if it is the original one or a replacement. I'm not sure if a pen made for a #4 nib could be equipped with a #3 as well. My 44, which should be very close in age to your pen due to its clip, has an original Supra nib, which has no size number but looks like a #4. My 222 has a replacement #2 nib but is slightly younger than yours judging from its clip.
Later, that is post-war, pens have a pretty clear numbering system. First digit is the model series, last digit the nib size, if it's 2-digit it has a steel nib, if the first digit is doubled, it's a 14k gold nib. The last pens made under the name of Osmia in the 1960s were the 66 and 77 Progress, which do not fit into the numbering system and have nothing in common with the Progress series of the 1930s.
But now to your pen: It looks VERY similar to the 222 model, the most significant difference is size. My 222 is only 111 mm long and made of a different celluloid. However, I have another pen branded by a stationary shop in Frankfurt/Main that showcases the same celluloid as your pen and, except for the clip and imprints, is almost identical with the 222. They even share the same threads so that I can exchange all parts between the two pens. Given that the DIN system of standards started in 1918, this might not be over-interpreted but it's still surprising.
One thing I noticed is that your nib seems to show a #1 imprint inside the diamond on the nib. So, what size is it really? Your nib imprint also looks different from any Osmia nib I've ever seen, actually older.
In any case, you've rot a really rare gem, congratulations!