Reading NSMB's TSA format?

I have been attempting to add graphics support to my editor, and I have got it to load graphics and TSA/Map16 data. However, I'm still having trouble with the format that defines what objects are displayed, where.
Can anyone help with this?

Here's what I've discovered so far: (Do note that all data to do with the grassland tileset, which I am using for testing, is stored in files named with some combination of "I_M" and "nohara".)
TSA data is stored in the 'bg_pnl' folder.
Object conversion data is stored in the 'bg_unt' folder. (There is a normal file, as in "I_M_nohara.bin" which I describe below, and another, as in "I_M_nohara_hd.bin", which I do not yet know the format for.)
Collision/behaviour data for tiles (I still need to research this) is stored in the 'bg_chk' folder.

What I'm mostly concerned with is the bg_unt folder.
I will explain the format of the normal, non-"_hd.bin" files (from what I know so far):
Each tile is 3 bytes long. (Although I have seen some that are 4 bytes long.)
After a tile, there may be an FE, which defines that the tile placement should go on to the next line.
After a FE, there may be an FF, which defines that the object is complete and another should be started.

Now! I have figured out that the TSA number seems to be the second byte in the 3-byte tiles. (I have not yet researched the 4-byte tiles too much)
Yet, I cannot correspond these to the actual TSAs.
If you would like a copy of the 2.1 beta to help me with this (which includes a tileset and TSA viewer, and a WIP (breaks on 4-byte tiles) viewer for this format) then PM me.

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I'll put something here later.