I tried version 17.x 18.x and 21.x on a TP-Link W8970 v1, all the versions seems that are experiencing the same problem with WiFi adapter not recognized (the device was working on OEM firmware).
Command lspci doesn't show the real Atheros AR9381 but shows Atheros AR5008
Command dmesg | grep ath doesn't show anything
Command wifi doesn't show anything
I fixed the issue rewriting the BoardConfig from mtd6 backup using kmod-mtd-rw.
Then I installed ath9k-htc-firmware and kmod-owl-loader and now everything works like a charm.