I have several dongles of various origin. A few of the original cheap non-TCXO from China (63 and 180 ppm drift, yikes), two of the v1 RTL-SDR.com 1.5 ppm TCXO, and two of the NooElec NESDR SMArt 0.5 ppm TCXO.
Instead of screwing around with them all having the same default 00000001 serial #, I've modified them all using rtl_eeprom. The NooElec are now 00000010 and 00000011, the RTL-SDR.com are 00000020 and 00000021, and the cheap ones reflect the ppm, 00000063 and 00000180.
I also disabled the IR receiver with rtl_eeprom, which pretty much guarantees that they won't show up as multiple BULK IN INTERFACE entries, instead showing up as a single RTL2838UHIDIR entry each.
Long story short, if you keep all of the serial #'s 8 digits long and put them in some sort of sequence, I've found that they will usually line up with Device 0, Device 1, etc. So in my case, Device 0 = 00000010, Device 1 = 000000011, Device 2 = 00000020, and so on.