I would suggest that if someone wants a piano that stays in tune for a
long period of time that they acquire an old Mason and Hamlin Screw
Stringer model.  They hold tune for a long time if climatic conditions
stay stable.

I was always told that one of the biggest reasons a piano with good
pinblock goes out of tune is due to the changes in humidity levels
causing the sound board to move or change crown.  It may not change
crown but can certainly add more pressure hence tension to the strings
or less tension.

Don Teach - Shreveport Music Co.
Shreveport, LA