That's what I'd assumed when I started skimming the spec, but the section I referenced seems to indicate a max of four regardless. I've never heard of a JPEG th

That's what I'd assumed when I started skimming the spec, but the section I referenced seems to indicate a max of four regardless. I've never heard of a JPEG that's not RGB(A) or CMYK. So it would be highly unusual, not saying it couldn't happen but given how unusual it would probably be replaced with a custom format for that specific application.