@snadge I'm seemingly successfully using it on a VMG-8924-B10A and have used its predecessor firmwares too (v24 and v21) when they were marked for 8394, but not overtly for 8924. v21 eventually found its way into the 8924 ftp, as you've found. The documents enclosed definitely make reference to both models.
I was hoping that v24 would cure the hellishly annoying random reboots that I am suffering from, but alas not. I'm turning my thinking now to a failing power supply. Unit is about 2.5 years old so given what I've read maybe I've done well to get this far...
Uncertain now whether to try and get a new PSU or try and blag a new modem / router from my ISP (Zen). We paid a £75 surcharge in July 2016 for this model because it was (allegedly) intermediate/advanced level rather than entry level and supposedly reliable. IMHO a router should last longer than a couple of years. Also rather tellingly, Zen are no longer touting Zyxel modems anymore, instead they seem to be pushing Fritz!Box. Can't say I'm enticed by the name. I think I already sort of have one, in this Zyxel!
I might try both... It would be good to have a spare VDSL modem anyway.