I didn't read through yet. But that is dun factor. You have barring on the legs, and what looks like masking on the shoulders and neck.
However, by the rules of IBHA, not a technical dun. Would be an appy with primitive markings.
IBHA does not recognize excessive white. And, less than half of the factor points for a dun normally aren't going to get a horse into IBHA. Ie: A dorsal stripe alone does not technically make a dun. But primitive traits.