I have a very oddly specific situational question;
Actually there is nothing odd about it, it comes up all the time.
In a civil lawsuit where a plaintiff is attempting to gain a sum of
money from the defending party, is the plaintiff and their counsel
allowed to change the amount sought, after the defendant has been
served a court summons (which has the damages sought stated on it). Or
are damages ultimately decided by a judge/jury and the damages sought
are somewhat irrelevant to a case? If this was in fact allowed, why
wouldn't the plaintiff always change the requested damages after more
evidence comes to light before a trial?
There are two rules involved.
If a default judgment is entered, generally speaking, a plaintiff cannot secure a judgment for more than was requested in the complaint that was served. So, if you think that the defendant might not answer and the original complaint was wrong, you need to not seek a default on the original complaint, amend the complaint and reserve the amended complaint.
The idea behind this rule is that the defendant should be able to make a rational decision about whether or not to fight a lawsuit based upon what is at stake in the lawsuit and not be surprised if the defendant decides to default to avoid litigation costs.
But, if a party answers the Complaint, then damages are determined based upon the evidence provided at trial and may ultimately be determined at trial to be either higher or lower than the amount claimed in the Complaint.
The idea behind this rule is that if the defendant had decided to litigate that the ultimate outcome should prefer reality to procedure since each party has input into how the decision is made by the court.
It also isn't uncommon for events that take place after the filing of the Complaint to change the amount of damages that are owed. Sometimes the damages go down, for example, if it is possible to mitigate damages in some way such as by selling defective goods that were delivered at a discount. Sometimes the damages go up, for example, because storage costs for the defective good that were received and are being held as evidence or for resale continue to accrue.