They will only know your visa has changed if you update address cetc. Happened with mine earlier this year - they took copies again and had to fill out forms (Not DTV)
It depends - an Embassy can put a note on a record. I mentioned one on here a week or two ago when Netherlands put a note on sopmeones and other embassies would not touch it. I had a reply from an agent who said that was possible but also alluded to certain embassies wanted a bigger controibution.
Are you sure the Embasy in Cambodia did not add a note to your immigration record for some reason? Might be an idea to contact an agent with the contacts to check this.