The tray...
I was fortunate in that my RR-2 was an all-original, low use model right out of Cedar Rapids, IA. It has the 'early style' tray that was also used in the 3's and 4's with the warning about not operating the microwave without the tray in place.
I've talked with the owner of an RR-1 but his was a curb find so he's unsure about whether his had a tray, or not. We also know there's an "early" and "late" version of the 1, but having not set hands on either, I can't say if the difference is purely cosmetic, or if glass was introduced mid-year. -Cory