The details appear missing:

1. UA has a ticket counter at PVG! It is facing the front entrace in the middle of the hall, several rows away from CA's check-in counters. I knew it since I used the couter for some ticket issues between UA and CA last year.

2. OP should have had a BP issued by CA in PEK, then he/she did not need to use the UA check-in counter at PVG. In the worst case, as other suggested, he/she should have got a BP from UA counter at PEK, which I had done it before too.

3. UA flight left during the day or maybe later in the day. I could not imagine that CA counters were closed. OP seemed should be able to talked to CA station manager at the time.

PVG is somewhat weird in that international luggage cannot be tagged to the final destination from another domestic airport or vice versa. In this case, OP had to pickup the luggage and re-checked at PVG. The OP did not need to use the UA counter at PVG unless he/she had checked luggage.

On a side note, if they knew that the 1st flight was or would be delayed, did they offer to put you on an earlier flight free of charge? There should be frequent flights between PEK and PVG that operated by CA.

It happened to me twice that they offered to put us on ealier flights for a subsequenct internatinal flight due to delayed inbound aircraft. In one incident, the ealier flight was about to depature in 20 minutes, and we made it. One of the counter person even dragged my luggage to a special location so that it could be screened and be loaded to the plane. I guessed that my UA status helped the situation. Does the OP has any status with *A?