I saw this thread and figured I better work on linking my two accounts. My MileagePlus account was "Firstname I Lastname, Jr." My OnePass account was in the name of "Firstname Lastname." I thought the "Jr." would be a problem, seeing this thread. I called CO anyway, and the agent thought it would be a problem, but she saw that my CO credit card had both the middle initial and the Jr., so problem solved.

She changed the name on the CO account to match the MileagePlus account and all was well.