I'll try and clear it up a bit.
The most reliable way to tell is 2 inductors, or a 175w power brick. That is the only way for sure. If you have 3 inductors, it's a zephyr board, but think about this. You can put a lower power 65nm in a 90nm socket! So theoretically if MS ran out of 90nm cpus before zephyr boards, they could be sticking 65nm cpus in the leftover zephyr boards.
The lot number is hit or miss, but the higher the better. There are zephyrs with lot numbers higher than falcons though.
Team FDOU got falcons earlier, but still have later lot numbers with Zephyrs.
The best way to check inductors is to look through the bottom vent with a flashlight with one eye closed. you'll see the three, or two with a with ring on the pcb where a third would go.
I have a lot 739 CSON dated 10/3/07 that IS a falcon, only 2 inductors, no heatpipes, and has the older 203w power brick. It's the only one with those stats that I've seen. I got lucky.
this site was for people to post xbox information for which dvd drive they have, but people are putting falcon status in the comments
http://www.360drives.com