Atlantic,
CLP is in charge of all W&B issues. The station inputs pax counts, cx values, etc. The gate then 'closes' its end of the deal - pax count, ACM, XFA, child weights, and what-have-you, when all known variables are input. Meanwhile, operations 'closes' out the cargo end with its final count of bags, mail, freight, etc.
THEN, CLP closes the flight and an ACARS message is transmitted to you with W&B data, based on the final px and cx values the station entered. If something changes - last minute bags, or px, or ACM ( B) ), the station must call CLP and have them open up the flight. The station puts in the 'new' final number, and the process begins again. The gate contacts CLP for px changes;operations contacts CLP for cx changes.
So while your arrival constituted a little extra work for the agent, it's not that big a deal, and in my view, the agent overreacted. Do keep in mind the pressure is on everywhere across the system for early closeouts and early pushbacks. We've pushed 15 minutes early, which would have left you on the outside looking in! Also, we have been directed, if bags are late into the make-up area, or if customers are tied up at security, we are to leave them behind rather than delay the flight. There is panic amongst the ranks not to have a delay pinned on you.
FWIW, I think the whole CLP deal is a fiasco. Why can't the stations close out the flight? We used to, and it's no big deal - and we still maintain our quals. CLP is just another middleman in the way. Here's a good example. If a flight arrives with more fuel on board than the departure release calls for, do I advise CLP? Noooooooooo, because CLP and dispatch got into a pissing contest. As a result, I advise dispatch of the correct FOB, they advise CLP, and CLP makes the W&B adjustment. Just more US Airways grade A bulls**t.