"Considering how he described his time there I am assuming it has branched off from our own. In Bulma and my time he was never in a coma. After we defeated Cell he returned back to his own time, though he showed up again years later when another threat came to his world." Really, time travel, multiple universes, it was easier just to go along with it rather than question it too much. Vegeta leaves that up to Bulma to try and work out the hows and whys behind that.

However, back to Yondu, and something that needed clarifying. "Mess up? Do you mean what the you has already done to this new son in his universe, or do you have concerns for what you may do with him here?" Not intentional mistakes, but they could still happen.