Yes, I know about the secret chain, and here's some more info.
Besides that 100,000 limit on chains, there's also a cap of 10,000 points per chain step. This happened in my second screenshot above: that value of Chain 970000 should have been more, but as a 97-step chain, it was capped at 970000. The previous step had been Chain 960000.
I also found that 10,000 cap in the code, and raised it. That allows chain scores on Stage 5 of over 1 million (yes, the display will extend to 7 digits - screenshot below.) But now it gets interesting. It turns out that the 10,000 cap is *also* used to control scoring for the red-blue-yellow secret chain. When I raised that cap, the secret chains became worth 10,000 per step *plus* the standard non-secret chain value, so it went like 10030, 20120, 30270, 40480, etc!
In other words, the secret chain is handled internally just by setting the current chain value to 10,000, then letting the 10,000-per-step limit apply to the scoring as you chain more yellows.
(In the unhacked game, you almost always run into the 100,000 limit before you run into that 10,000 cap. The only exception is in Saturn mode, Stage 6, at boss W(--)W on the second set of enemies, where they appear in a circle and fire at the center. Those ships are worth 10,000 points each, so if you kill three of them, it should be Chain 30000, but the cap limits that to Chain 10000. This only matters if you died or failed to chain the first set of W(--)W, because otherwise you'll reach the 100,000 limit instead.)
http://www.dos486.com/misc/chain1197040.jpg
It's pretty simple to do: extract the game files off the CD, load GAME.BIN in a hex editor, search for the first occurrence of 100000 (in hex with Motorola big-endian byte order, it's 00 01 86 A0), and change that to a larger number. There's separate copies of GAME.BIN for Arcade and Saturn modes, in the STV and SS directories.
