Here's an interesting data point. I had a flight in December which was paid for with a United Explorer card a few months back. Those benefits: only 1 free bag, 50 lb. limit.

In mid-December, I upgraded to a United Club Card, which comes with 2 free bags. I had thought the benefits would have been coded to the Explorer Card used at time of purchase, though imagine my surprise when I checked my baggage allowance right before taking the flight: the Club Card benefits kicked in and I had an allowance of 2 free bags!

So your upcoming flight very well may be enabled with Premier access. I hope so. Get in that United Club! Enjoy!