The sequence is because Google uses binary diffs for their updates.

The latest release candidate (?) is FRF83. You can download an update.zip from http://android.clients.google.com/packages/passion/signed-pa... (requires updating to FRF50 first).

You can check the build in Settings -> About phone -> Build number.

OK, so I could also install FRF83 directly without going through the updates?

No, FRF83 has been published only as an update from FRF50 (using the link above) or from FRF72 using http://android.clients.google.com/packages/passion/signed-pa....

If you are running the stock Android 2.1 image, you'll receive an over-the-air update whenever Google deems it ready for general release. Or you can update your phone now to FRF50 or 72 and then to 83.

Thanks - so I guess since I have installed some Froyo image before, I will never get a push from Google for the final release anymore?

If you installed one of the Froyo updates direct from Google, then you will continue to receive future updates. If you unlocked your phone and installed a modified or custom image from another source, then that image probably has OTA updating disabled and you will need to apply updates yourself.

If you flash back to a stock image from Google, then I believe you will start receiving OTA updates again.