How long do you think Black was standing there for before Shin died.
They two Trunkses in the new timeline probably free Old kaioshin and so on and have split the timeline before fighting Babidi, but assuming Black was already snooping around would Black be duplicated when the two Trunks create a paradox big enough to split the timeline?
In the cell saga the cells timeline trunks gets duplicated into the old main timeline when Cell emerges and splits events off from the Unseen timeline. When he goes home later than he originally would And kills the androids in combat and then cell, he creates Trunks timeline splitting off from cells timeline.
Would black be duplicated here? What'd happen when he tried to leave to another timeline?
Or would this Black not show up in the double trunks timeline at all. In the same way cell wasn't in the unseen timeline and the old main timeline? Black can only show up once as there's only one of him, Trunks only got duplicated because cell travelled back further than Trunks.