I'm running a custom snapshot build (r17525-a46fa5c3a7) I did last week (Sep 16) for the Archer C6 v3.2 (mt76).
I've noticed that there is one Wi-Fi firmware in the OpenWRT builds that is outdated when compared with the file from the upstream repository.
See below the files installed in the router:
root@ap2:/# ll /lib/firmware/mediatek
drwxr-xr-x 2 root root 185 Sep 16 02:59 ./
drwxr-xr-x 3 root root 94 Sep 16 02:59 ../
-rw-r--r-- 1 root root 122644 Sep 16 02:59 mt7615_cr4.bin
-rw-r--r-- 1 root root 457992 Sep 16 02:59 mt7615_n9.bin
-rw-r--r-- 1 root root 11102 Sep 16 02:59 mt7615_rom_patch.bin
-rw-r--r-- 1 root root 335072 Sep 16 02:59 mt7663_n9_rebb.bin
-rw-r--r-- 1 root root 440568 Sep 16 02:59 mt7663_n9_v3.bin
-rw-r--r-- 1 root root 278558 Sep 16 02:59 mt7663pr2h.bin
-rw-r--r-- 1 root root 209230 Sep 16 02:59 mt7663pr2h_rebb.bin
And these are the files from https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git:
dimitri@dimitri00:~/src$ ll linux-firmware/mediatek/mt7663*.bin
-rw-r--r-- 1 dimitri dimitri 335072 Sep 23 21:35 linux-firmware/mediatek/mt7663_n9_rebb.bin
-rw-r--r-- 1 dimitri dimitri 441688 Sep 23 21:35 linux-firmware/mediatek/mt7663_n9_v3.bin
-rw-r--r-- 1 dimitri dimitri 278558 Sep 23 21:35 linux-firmware/mediatek/mt7663pr2h.bin
-rw-r--r-- 1 dimitri dimitri 209230 Sep 23 21:35 linux-firmware/mediatek/mt7663pr2h_rebb.bin
Notice that the "mt7663_n9_v3.bin" file size in the the kernel repository is bigger, which seems to be newer that the one in the OpenWRT repository but I am not sure.
So I am just sharing here my finding so any OpenWRT developer can confirm.