Okay I knew there was something going on when I saw two logos in VRAM. I had one of the compressed data locations wrong, here's the update
*stars title screen*
$B8:9458 0x1C1458 map data: BG1 title screen logo
$9B:C0A9 0x0DC0A9 graphics: stars background
$9E:AB47 0x0F2B47 graphics: title screen logo (stars background) (336 tiles?)
So yeah the tiles are sitting there uncompressed in ROM. But you see there are two separate logos, each slightly different if you look side by side. So if you want to make another awesome title screen just slightly different, you can put it in the game. I would recommend just reusing the same tiles because nobody's going to know
So a few things to note. Even though we can shove lots of new stuff into expanded ROM space, the programmers packed the RAM quite well, which would require more deep ASM mods to overcome. So there's enough room for 348 unique logo tiles
on the blimp screen (not counting the blimp tiles, just for the logo). Since we have the map data it's actually pretty easy to put tiles anywhere you want on screen. You could even use the blimp tiles for the logo, but you'd have to get creative to have the blimp show up with missing tiles. So make sure there's no more than 348 tiles on the blimp logo.
On the stars background I counted 336 unique logo tiles (including the TM) but I could be wrong. Just make sure to not use more tiles than the original because they won't fit into VRAM without more creative mods.
Also you see the logo uses 3 palettes total. Each tile can be told to use a different palette in the map data. Map data is 2 bytes per tile. Lower 10 bits are the tile number, next two bits is palette etc like this: yxPppptt tttttttt vSNES can really help show you all the data in a savestate on either title screen.
Each BG Map Entry consists of a 16bit value as such:
Bit 0-9 - Character Number (000h-3FFh)
Bit 10-12 - Palette Number (0-7)
Bit 13 - BG Priority (0=Lower, 1=Higher)
Bit 14 - X-Flip (0=Normal, 1=Mirror horizontally)
Bit 15 - Y-Flip (0=Normal, 1=Mirror vertically)
There are many talented romhackers around here, maybe someone else has some good ideas to help too?
Keep up the great work!