The dataplate isn't very clear - I did some stretching and pulling with photoshop to try to get the detail out.
One thing is clear - it's got a rating for both 50Hz and 60Hz. From the more legible 60Hz data I can get it sorted out.
I believe I can read "1000 r/min" on the lower right but it is more likely to be "1080" or "1088". Either way these are 10-15% below "1200" which would correspond to a 6-pole motor.
Interesting: Motors should run at the same Volts/frequency ratio. If it's designed for 50Hz with an input of 420V, then that ratio is:
420/50 = 8.4
Using that ratio when running on a 60Hz supply:
8.4 * 60 = 504V
But that's not on the label, and neither you nor I have ever heard of a 500V AC supply. That said, I would expect to see a 480V rating, which is close enough. But actually the rated supply voltage for 60Hz operation is "440V" on the dataplate.
I think they built this motor to tolerate a lot of very poor power supply possibilities. You see some "high-efficiency" motors with specs on the dataplate that require a perfect 240V/480V power supply to get the rated power. Fair enough but in reality your motor doesn't get a nice perfect supply most of the time. The builders of this motor were probably aware of that and decided to put realistic values on the dataplate so the person using it wouldn't have to de-rate for losses.