I guess that your not going to get a better response than from Kerry himself!
It's all 304 series stainless steel, so you should have no corrosion. Did it get dinged or something perhaps? The inlet has 3x slots that help compress it onto your collector when the clamp is tightened. You should simply be able to "wiggle" it back and forth slightly to help open it up and slide it off. You could also tap on the centerstand stop/bracket edge while pulling back. Honestly have never heard of anyone having an issue removing it. If it slid on, it should slide off
Just a thought but you may be able to heat the mid-pipe where it overlaps the header pipe with a propane torch enough to expand it a little and then try tapping it back or wiggling it free.+1
Remove the clamp completely as it has a tab that fits into the inner pipe that you probably did not notice.
Fretka