Today I briefly did a double check on the inheritance of the manchado pattern (a very rare pinto pattern!) and instead came across a blog post from the Equine Tapestry (a great horse color genetics blog I've followed for years) about how seal brown probably isn't an Agouti allele which I'd totally missed.
So anyway now I gotta change the seal brown genetics in my horse breeding tool I guess.
for those who don't know; genetic linkage is when two loci are close together and their genes become linked in pairs that are always inherited together, aka why tobianos, roans and sabinos might only pass down their white pattern to black offspring and never chestnut ones.