Added the effect durations to modifiers.txt, the rest were there.
I also noticed that KoL itself doesn't list the effects from chewing wads, and submitted a bug report.
On the twitch show, Jick said that spleen items had to be added individually, rather than being normalized like potions.
Given that Jick specifically said that they were hardcoded, I don't think it is "debatable" that they are hardcoded, eh?