Brian D: the Yashica 12 was 120-only, the Yashica 24 was 220-only, and the Yashica 124 was a contraction of the two names, meaning you could choose between 120 and 220!
My first medium format cameras were a pair of Yashicas -- a rough LM and a slightly less rough 12. I bought them because I was disappointed at the results I was getting from 35mm film and when I looked into the photographs that I loved, I learned they were shot on medium format. Well, coming from a Spotmatic F and a Nikon F80, these Yashicas were quite a puzzle. Especially since these Yashicas were in sad shape, probably unused for 20 years, and had stiff/seized parts. I decided to sell the LM and keep the 12, because it was newer and had modern shutter speeds. I should have kept the LM, because the lens was better. Even after a CLA I ended up selling the 12.
Fast forward a few years, and my dad found another LM at a flea market. It was covered in grime -- and I didn't think it was very promising. Well, the grime seemed to actually protect the camera. After a thorough cleaning this LM looks like new. I shot a test roll, and the Yashinon lens is delivering the amazing quality I remember from my first LM. Most of the shutter speeds were good, but the slow speeds are sticky so I have sent the camera for a CLA.
Since I started with those first Yashicas, my arsenal has expanded (including a Bronica kit and a Rollei 2.8f) but I am looking forward to keeping and using this second-chance Yashica for a long time.