Here is just my own observation, though it would be probably better to post it at PPG forums. I noticed that the following with respect to spells doesn't necessary add the descriptions:
SAY UNIDENTIFIED_DESC ~Unidentified Description~ // unidentified description for items, spell description for spells
SAY DESC ~Identified Description~ // identified description for items, unused for spells
If you look into NI then after compiling this part you would see something like this:
Unknown - Offset 0x42 - 00 00
Unknown - Offset 0x44 - 00 00 72 62 00 00 55 6e
Unknown - Offset 0x4c - 00 00 00 00
Description - Offset 0x50 - No such index (-1)
Unknown - Offset 0x54 - 63 40 01 00
Unknown - Offset 0x58 - 00 00 69 66 65 64 69 74
Unknown - Offset 0x60 - 00 00 00 00
I think SAY UNIDENTIFIED_DESC should extract offesets 0x42 - 0x4c, and SAY DESC - 0x50 - 0x60
This is all because someone has assumed that the structure of ITM ans SPL is identical while in my humble opinion it is not. Please correct me if I am wrong.