just register as a developer, no strings attached, just create an account and you can download all os recovery images
i moved up all the way to 2.2.1, then reinstalled 1.2.1 because i wasn't liking lollipop
also unlocked the bootloader, flashed CWM and rooted
now i want to try the BitO kernel, which is only available to 2.2.1, so installed the 2.1 update (through CWM, as i forgot to flash the stock recovery for 1.2.1)
now i try to install 2.2, but recovery gives me an error

flashed CWM again, doesn't want to flash the OTA
flashed the 2.1 stock recovery, it starts the update but almost immediately gives me an error
yes i could flash the 2.2.1 OS recovery image, but then i would lose all my data....
EDIT: never mind, fixed it, flash boot.img, recovery.img, erased system, flashed system img, all from 2.1 update zip file, reboot, now 2.2 is installing through OTA