If the charges were separate, I don't know why you cannot request expungement of your record for that particular charge.

The best thing to do is to go to the courthouse and ask them when you get a copy of the form ( if you are going to do this yourself )--note, this is a request for PROCEDURAL advice, NOT legal advice since obviously, clerks don't give legal advice any more than they change birth certificates without court orders. I don't know who is telling you this other information--but ask them where their information is coming from and decide if it is a reputable source.

Good luck.