In snapshot 21w17, signs are completely missing the 'Lit' tag, preventing them from glowing
Glow ink sacs and regular ink sacs will be consumed and play the sound, but no tag is changed since there IS NO TAG!
Judging from snapshot 21w03a, that is how they work (using a tag)
In 21w10a, the lit state was changed from a block state to a NBT tag to fix MC-212168. Invalid.