Took another look at Castlevania III. I originally set this aside because I thought the issue was MMC5 and there weren't any test ROMs to pinpoint the problem. However in thinking about it it should have still worked in the range of IRQ timings I tested, so I thought maybe there was still some DMC edge case I was missing.
It turns out that there is a single instance where the game reads from the APU status register ($4015) at the same time the DMC channel decrements to zero. Originally I had this read back as not zero, but it turns out to be correct to have it read back as zero. This combined with adjusting the IRQ timing led to the run working on console. I am up to getting Grant, hopefully I'll have a complete run in the coming week.
EDIT: It now desyncs after the wrong warp. Lot's of crazy stuff is happening there, could be anything going wrong. Probably the new last boss of NES console verification outside of resets.
