lua filesdatainfoaccessoryid.lua
-ACCESSORY_Sapling_Hat = 9215
+ACCESSORY_SAPLING_HAT = 9215,
lua filesdatainfoaccname.lua
-[ACCESSORY_IDs.ACCESSORY_Sapling_Hat] = "_Sapling_Hat"
+[ACCESSORY_IDs.ACCESSORY_SAPLING_HAT] = "_Sapling_Hat"
idnum2itemresnametable.txt
-9215#sapling_hat#
+9215#Sapling_Hat#
Basically, the ACCESSORY_ID stuff in the LUA's needs to be capitalized. (At least, I'm pretty sure. I think I had issues in the past cause of that.) The end part doesn't, it just needs to match exact case of the sprite files.
If not, and more importantly, are the sprites named _sapling_hat.spr or _Sapling_Hat.spr? Because you have the sprite set to Sapling_Hat in the LUA, but in the resname table you have it sapling_hat. Assuming it is _Sapling_Hat, the above corrections I made are right. Otherwise, resname table is correct and you need to change accname.lua to lower-case.
Also, to make sure you at least have the LUA side working, you can always test @changelook VIEWID (in this case, 9215), if sprite shows up LUA is fine and you know the data is wrong. If it doesn't show up, LUA is wrong, data MIGHT be fine, or data is broken too.
Unrelated to problem, since you mentioned client, without editing anything with packets and such, just a regular checkout of rAthena, you can use up to client 20110810 btw. With that client, I've had the least ammount of errors and such, new mounts work, Archangeling Wings/Traveler's backpack work, etc. Just in case you wanna try it.