Maybe the way I describe wasn't clear enough, I'm not trying to glamour A > B > C as in A > C. Put it in a clearer way, say I glamoured Gae Bolg (i80) on Darklight Spear, then Darklight Harpoon over Gae Bolg Zenith (i90) in an attempt to indirectly glamouring Gae Bolg (i80) over Gae Bolg Zenith (i90). When I tried doing that, what used to happened was that Gae Bolg Zenith (C) would take the appearance of Darklight Harpoon (B) instead of Gae Bolg (A). I believe this is working as intended, where if you tried to glamour an item with another item that is already glamoured, it will take the look of the base item. However, this is no longer possible now. If you try to repeat the process, you will get an error message of "Glamours may not be stack.".

TL;DR, you can't glamour a gear with another piece of glamoured gear.