What's the significance of Netgear TA Numbers?

Two different TA Numbers (100-19785-01R20; 100-19785-01R21). Same model router: Netgear R7800.

Any way to find out how R21 (which I assume means revision 21) differs from R20?


Given the point that those numbers yield no results in a google search, it's likely that they are serial numbers and not model numbers. Therefore what they are is not significant.