I've always taken an older one to the airport(s) with me, budgeted extra time to go to the CBP office first (often the very same people, we recognize each other,) and then they write up a new one. 5 minutes. Never a problem. 10 min once when the officer on duty was on break. They do look at SNs of any personal property listed on the form (incl. cameras, laptops, etc. if desired. Cash, if over $10K (incl. >$5K if fam members are carrying the balance of it.) IF you have something brand new...i.e. fancy camera, also list it on the form.) Is there some problem all of a sudden whereby you can't get it done real-time (immed. prior to departure?)