The way my tuner once explained it to me:
Pianos will vary in total pitch over time and the seasons. In the winter, low RH dries the wood and the piano drops in tune a few cents on the whole, and in the summer it goes sharp a bit. As long as everything moves together, it's fine and doesn't sound out of tune.
So a piano may be tuned to 440hz, and by the next tuning, it will have settled to 438. Particular strings may be more out of tune from the whole and these are the ones that beat, sound off, etc. So on a given tuning, the tuner doesn't just set everything back to 440. If it's in the winter, they'll use a 438 as the baseline and tune everything to that, on the understanding that later in the season the pitch will rise naturally as the wood swells.
But if you actually want a true pitch raise, either because the baseline has dropped, or you just prefer it higher, then the tuner will go through and reset each and every string to your preferred pitch. And since this typically involves changing more tension on more strings, it could require a few passes, or a touch up days/weeks later, depending on how picky you are and how your pins sit.
When I got my piano, it was supposed to be tuned to 443 from the factory. The first tuning found it around 440. My tuner recommended waiting a year to see how it naturally moves before a full pitch raise (maybe it was seasonal fluctuation and will raise on its own). After a year and a half, it was down to 439 or so, and at that point I opted for a pitch raise with a touch-up afterwards.
I missed my last tuning session and my tuner is actually coming in this afternoon, so I'll see what has happened in the last 12 months. If anyone has any questions I'm happy to bring to him.