I've never heard anything about the quality varying year to year. I think people are just amazed how great they are for their age. The 221 is the regular featherweight. The 222 is the freearm. Here's a link to a site with a lot of info:
http://www.singer-featherweight.com/...cts-Myths.html
Mine is a 1946 model 221. I love it! I use it for all of my piecing.