Stored accordions and deterioration

[Rafael]

It is well known that accordions do not do well when kept stored in their cases for long periods of time. However, in multiple cases, instruments are advertised for sale as being in supposedly optimal conditions because they have been kept stored and untouched for years. Assuming that they were kept in optimal conditions of temperature and humidity and protected from dust, what would be an estimated amount of time before the instrument begins to suffer deterioration?

 

[Ventura]

in the temperate zone, we have seen accordions
simply stored deep in some closet on the main floor
of a typical house come out of their case looking great
and playing quite nicely after 50 years or more

this environment prevents drying out, but low moisture
so no mold or mildew either.. i have popped bellows
on student 120 bass 3 reed models and the reed
leathers are still supple and decently flat.. a bit of
Lexol rejuvenates them just fine.. but check the
backstraps and treat the stress points where they loop
or just replace the straps

it was student models that tended to get stored and forgotten
after the son or daughter got older and distracted by Life

i doubt in the Tropical zone this could be possible..
as things get hot and dry in all corners of a house