This is somewhat related, just because there is a hardware table embedded in this thread, even though I am running DD-WRT instead of Merlin.
I just bought a RT-AC1900 with the following details:
Model: RT-AC1900
FCC ID: MSQ-RTAC68U
Base Firmeware: 3.0.0.4.380
H/W Version: C1
Could not flash...