More specifically, inscribable versions of items that are normally non-writable are writable due to oversights on the part of the game designers. For some monsters these, the drop updates have not been updated. This is normally the case when a monster is integrated into a campaign other than the one it originated from. It is the instanced area, linked to the campaign, that will determine whether or not objects are inscribable.
Also this was the case for the 2010 Halloween mausoleum quest. The instanced area was defined as part of a campaign where only non-inscribable drops could be obtained. However, monsters could drop non-inscribable spears and scythes. These monsters were also linked to the NF campaign in terms of drops and normally only drop inscribable items. This also caused a bug with items with an additional bonus. Unfortunately, this is not the case for inscribable weapons of NF.
For example:
- Terrorweb Dryder in NF/Realm of Torment = Eternal Shield, Eternal Bow, Storm Bow, and Ghostly Staff.
- Original Prophecy Titans, but found in NF/Realm of Torment = Magma Shield (see other?).
- Obsidian Furnace Drake at NF/quest: Drakes on the Plain = Shadow Shield (see other?).
Note: Just like the non-inscribable blue Eternal Shields, the inscribable 8/15 and 8/16 versions rarely come with a inscribable slot, unfortunately.