My wifes great-grandfather served with the 41st New York, and I have been trying for the past several years to find out if he was on active duty and with his unit at the time of the Gettysburg campaign. There is some question about this because he was injured during the winter of 1862 and then I have no record of him again until August of 1863 when he was put in the brig for losing his rifle. I have seen his pension records, I have checked the morning reports at the National Archives (many pages missing, including those of July 1863) and I have checked with the New York state archives to see if they had any record, which they didn't. I believe I have exhausted all possibilities, but if anyone else has any idea of where I could check, I would be grateful for that information.
There is actually a Richard Priester (or something like that) listed in that data base and I believe that is him, just a misspelling. His pension records definately show him as having served as a private in company E of the 41st New York.
Ah- a different spelling- the bane of genealogists everywhere. Yes, I see a Richard "Preisser" in Co. E of the 41st NY. Someone got a little careless with a: "u" and it became an : i."
As far as your original problem goes- without duty rosters it might be difficult to determine whether or not your man was actually at Gettysburg. It is possible that he is mentioned in someone's personal account of the battle, a member of his company perhaps. Its also possible that he is mentioned in some unit history.
Here are some possible sources (scroll down). You might take a look at the books by Field and Sturcke, or Martin, or even Heusinger (how good is your German? )