I had the same situation happen to me. When I booked the tickets through my corporate site, I entered my OnePass number but it defaulted to my MP number. This happened back in July and I decided at the time not to worry about it. I realized recently that I was close to Platinum status so I decided to move the miles over. I had United remove the miles from MP account and then I submitted a missing mileage request through email to CO (with my ticket and boarding passes but no screenshots). CO wrote back saying the miles had been credited to UA already and they could not credit to CO. I wrote back explaining that my UA number had been assigned by accident and that I had successfully requested UA to remove the miles from my MP account. A few days later the miles were credited. Not the quickest process so I would start sooner rather than later.