OK here's my explanation for how the title screen tile map works.Part 1: The Tile Map
The tile map in the ROM is at address $1FEE5, and it looks like this:
93 13 13 28 13 13 13
13 2C 2D 2E 2F 30 35 36 37 13
13 38 39 3A 3B 3C 3D 3E 3F 13
13 40 41 42 43 44 45 13 47 13
13 46 2B 2A 29 48 49 13 13 13
93 93 13 13
93 93 13 13
93 93 13 13
Each of those bytes (with the exception of $93) corresponds to a 16x16 meta tile (four 8x8 tiles).
$93 is a special case. It's actually just $13 with the most significant bit set (so 10010011 instead of 00010011). When the most significant bit is set the tile gets repeated a predefined number of times. In this case it gets repeated four times. You can change the number of repeats by changing the byte at $1FBB1 from $04 to whatever. I left it at $04 for my title screen. I don't know for sure if that value is shared by other tile maps or not, although I suspect it's not.
This image shows how the tile map corresponds to the tiles on the title screen. Apologies for the ugly graphic. I actually made this for myself as I was figuring this out.Part 2: The Meta Tiles
There's a table of meta tile definitions that starts at $20C1A in the ROM. Each meta tile definition is six bytes long. The first four bytes define which 8x8 tiles are used. I'm not sure what the last two bytes are for, but that didn't seem to matter for my purposes.
I actually expected the tile ID bytes to be references to the tiles in VRAM, but they're not. They're references to the graphics data in the ROM. The game actually seems to decide which tiles to load into VRAM based on which meta tiles are used. There's some wasted space among the title graphics, so you can potentially use more tiles than the original title did.
The meta tiles used on the title screen are $28 through $30, and $35 through $49. $28 starts at $20D0A. $35 starts at $20D58.
This is what meta tile $28 looks like in the ROM:
The first two bytes are the top-left and top-right tiles. The third and fourth bytes are the bottom-left and bottom-right tiles.
This image shows how the tile ID bytes correspond to the graphics data in the ROM. Again, sorry for the ugly graphic. I didn't label every single tile, but I think you can see the pattern. $25 is a blank tile that isn't pictured here because its not specifically part of the title graphics.
I think that's pretty much it.