As mentioned, flight number doesn't matter - ticket stock does. You would have to book directly with United to get 016 stock. If you must ticket through a corporate TA, an 016 ticket may not be possible.

For premier qualifying miles (PQM): same on both stocks
Premier qualifying dollars (PQD): zero on OS stock, the full fare on UA stock
Redeemable miles (RDM): a percentage of the actual flight distance on OS stock, and a multiple of the fare amount on UA stock

If you're US based going for UA status, you probably care about the PQD and want an 016 ticket. Otherwise it's not a big deal.