My wife was a 24 year overstay, she had her greencard approved 4 hours after interview. (new card being produced) I dont think your overstay is related to the delay. I think it has more to do with background checks and such do to your line of work. Due to your age and Irish citizenship you were around in the days of the IRA and a lot of other firearms related gunrunning and such. ( we had a Boston Irish gang running Guns back in late 80s and early 90s) Maybe that is the extra checks. With the expedite was not time to run them. Its a lot harder to take the green card away after its issued .Another reason is that your in a busy office..... I'm sure that has a lot to do with it. You will also find USCIS marches to the beat of their own drum and its hard to gage your case with others in your same shoes. Each case might appear to be similar but are so different once all the issues are broken down. Good luck and be patient.