I have a MC7710 cards which with the latest firmware >=year 2012 is not functional after cold boot - if it was plugged in USB before power-up!
I am running Linux, so loading sierra.ko should be enaugh to talk to it over serial, but after cold boot it is just silent.
Also I did test with multiple cards on different hardware with different OSes (all Linux based so I can’t tell anything about windows).
Evidence is pretty solid, below is info from one of the failing cards.
Downgrading firmware is not an opion, because people are getting OTA upgrades.
Manufacturer: Sierra Wireless, Incorporated
Revision: SWI9200X_03.05.19.04ap r5475 carmd-en-10527 2012/09/17 17:57:14
IMEI SV: 13
3GPP Release 8