That isn't uncommon due to partnerships. If you live in Mexico and want to go to France, for example, you might go Air Mexico-->Delta-->Air France, and that last flight would have 3 flight numbers.
I've flown exactly four times. To SFO and back; to one of the DC's and back. Age 9 or 10 the first time, 14 the second. I don't exactly see much of air travel. 😀
Codeshares: This flight marketed as a codeshare flight by the following airlines: (CO) Continental Airlines 6374 (NZ) Air New Zealand 9504 (US) US Airways 6334