There's a postjust asked three days ago about the same, but you have another question so I'll repeat and answer.
1. The 17 and 22 were officially introduced at SHOT Show 2010 on January 19th. There were leaks of pics and info in December 2009 though.
2. As alinero718 mentioned all Gen4's will say so right on slide. Gen3's will look similar, without the Gen4 marking, adjustable backstraps, and only a single recoil spring. Gen2's and Gen1's won't have the tactical rail and they don't have the finger grooves. Gen1's have a smooth grip finish and the Gen2's will have a more textured finish on the front of the grip below the trigger guard. The Gen2 serial numbers start at FG000 in 1988 and Gen3 in 1998.