I worked under a tech at a Steinway dealership for a few years. He did most of the concert work but occasionally had me doing stuff to help him out.
One thing I remember that he tried to drill into me was that when I went to do a "concert tuning", that I needed to spend some time figuring out what did NOT need to be retuned. Often, it was a big part of the piano that needed to be just left alone. He insisted that if the piano had bounced down the road in the big truck, been set up on a stage, beat on for a rehearsal or two, and still had notes that were in tune, DO NOT TOUCH THEM! If something needed touched up, typically a few unisons, do that. But when something is in tune and obviously stable, don't mess with it. That was his message to me. Probably somewhat dependent upon the context.
More specifically to your question, though, the humidity control probably has way more to do with your tuning stability than you give it credit for. I once had a regular tuning in a church where the sanctuary was totally interior and very tightly controlled in temperature and humidity 24/7/365. I didn't really want the job at the time but took it on because of several people who came before and their tunings just were not holding. So they asked me to have a look. I did a careful tuning and ended up looking after that piano for several years following (until we moved away from the area). It was extremely stable. I'd have a look about every 3 months or so and there were quite a few times when all I would do would be touch up a few unisions and call it good for another 3 months. Seriously, I felt like that was a case of "if it's not broke don't fix it." And it served me well in that situation. It was rare, I can't recall any other situation that dramatically stable, but it does happen.