Sgian Dubh
>I suspect what you're experiencing or obversing, Wiley is a combination of a fairly equable climate, conditions maintained in offices and residences in that area, and the water vapour blocking effect that polish has on wood. Add all this to hysterisis, and, as you surmise, I think what's happening is that swings in wood MC are reduced due to all these factors.

A useful generalisation is that it takes a change of between 3% and 4% in wood MC to cause an average 1% change in wood dimension. Therefore if you have a drawer front that is 100 mm tall (about 4") at 12% MC, then reducing that MC to between 8% and 9% will result in the drawer front shrinking in height to 99 mm (whatever those figures equate to in Imperial measurements.) That's not a very big amount really, and if the change in MC is delayed somewhat due to hysteresis and the effect of polish, then perhaps as you surmise, the season changes before the effect is fully felt.

I think it can be a bit of a mistake to slavishly follow the changes that could occur in the least favourable conditions. For example, I think most of the figures used in many charts and replicated in various ways in online calculators such as the Shrinkulator use numbers to be expected if bare wood is exposed to changes in RH.

On the other hand, I think it's imprudent when building furniture (for indoor use for example) to ignore the extremes that could occur. For instance, I always tend to build indoor furniture on the basis that wood just might experience an MC range from about 7% to 14%. Also, the rough rule of thumb figure I gave above (1% change in width per 3-4% MC change) is too much for American mahogany, and too little for European beech or European/American white oak.

All these factors need to be accounted for in the planning stages. Slainte.