Customer says the piano has never held tune. Tuner says he found it at A = 442 a year ago and tried A = 435. The tone doesn't indicate any bridge or soundboard problems.
This logic escapes me. Seasonal changes can move a piano 12 cents between winter and summer, depending on where you have it. I don't suppose Miami has the same swing as Minneapolis, so that has to be considered. If I found a piano at 442, in the middle of summer, I would tune it there. However, I don't ever see a piano that is equally off pitch, so it may be at 442 right above the bass break, 440 in the middle, and 441 in the top, so there is an average line that extends through the span. Perhaps a year of 441 in humid seasons and 439 in winter would give a baseline, but moving things 30 cents flat, all at once, will probably de-stabilze everything for a full cycle.
It seems that the piano may have gone way sharp before he tuned it down, and then went to the other side of the cycle and dropped below. We have had long threads of floating pitch on this forum, so there is some research material for those interested.
I have also noticed that flat soundboards, or those with no real bearing, will cause wild swings not only during seasonal changes, but also during tuning. I have assumed it was because it takes little change to move the initial tension changes from a straight string to one with bearing.