- Photo #1 is a 15-90 from the late '40s to mid 1950s. Judging by the striated faceplate & inspection plate I'd guess the serial numbers start with AK-, AL- or AM-. Note that it has an aftermarket light (giveaway red switch) replacing the original.
- #2 is a 15-91, or a 15-90 that has had the motor stripped from it. I can't tell the year as it's missing the plates and I can't make out the serial number.
- #3 and #4 appear to be the same machine, a 15-91, I'd guess from the early '50s. Note that the power cable has been replaced at some point, as you can see brown wiring going into the terminal plug.
- Photo #5 is a Singer 206, their first domestic zigzag. The machine in the photo is from 1953--if my eyes are correct, the serial number starts with EJ--and based on that prefix, the machine was made in Kilbowie and is one of the aluminum ones. That will make it easier for you to tip the machine back in a cabinet, as you'll need to do; tipping it back is the only way to access the bobbin on this machine.
- The machine in photos #6 and #7 is a Singer 15-90, though I've certainly never seen one in that color; judging by the paint quality, the machine was almost certainly painted after purchase, as no Singer came out of the factory looking like that. From the photo I cannot tell if the Singer decal on the arm was masked off for painting or added after the paint job. The faceplate indicates this machine is from the 1930s or early '40s, assuming that's the original faceplate, and you can see the original motor has been replaced with a white-colored aftermarket motor.
- Finally, #8 is a crinkle-finish model 66 with backtack. The chromed handwheel and non-marked tension dial, assuming those are the original parts that were on this machine, indicate it's from the 1930s or early '40s.