To be honest I haven't either. Usually it has been *A everything plus 1K at the same time. When I boarded yesterday at EWR for a 6am flight, however, they specifically called *A Gold by itself. I was on the jetway before the next group was called.
I assume this was because the flight was heavy with status'd fliers.
UA always boards *A and 1K at different times.
They go like this:
Global Services/First Class
1K/
Business Class* *(if flying on a three-cabin aircraft)
Through the regular lane:
Premier Executive (1P)
*Alliance Gold
Boarding Group 1 includes:
Premier (2P)
Premier Associate (3P)
*Alliance Silver
Boarding Group 2, 3, 4