The rule of thumb for air drying lumber is, of course, a year per inch of thickness. While the finishes we use do not completely block moisture absorption they do delay the transfer into the wood so I would assume they also retard it leaving. So it could be awhile.
With respect to old furniture I would only say I have not personally examined any pieces I would want. It might be built with finish on only one side but it may also have been a finish that did not do much of anything to block moisture anyway (like linseed oil). I've seen many pieces with poor fitting pieces, pieces that have split due to improper construction and pieces with warps. Warps may not always happen, the top of a dresser can be firmly attached to the sides and may minimize any warping to the point it is not noticable.
We are all free to build furniture as we see fit but I have been finishing both sides at least similarly for several decades now and I am quite happy with the results. I definitely would not have done my 10 foot dining table any other way. When you know that doing it the "other way" leads to issues like this chair, why do it that way? Doesn't make sense to me.
With respect to old furniture I would only say I have not personally examined any pieces I would want. It might be built with finish on only one side but it may also have been a finish that did not do much of anything to block moisture anyway (like linseed oil). I've seen many pieces with poor fitting pieces, pieces that have split due to improper construction and pieces with warps. Warps may not always happen, the top of a dresser can be firmly attached to the sides and may minimize any warping to the point it is not noticable.
We are all free to build furniture as we see fit but I have been finishing both sides at least similarly for several decades now and I am quite happy with the results. I definitely would not have done my 10 foot dining table any other way. When you know that doing it the "other way" leads to issues like this chair, why do it that way? Doesn't make sense to me.