I do have a couple of bows 10 years and older(one about 20),, but they are not really well made,, they shoot pretty good and have not gone up in weight,, when I made the bows in a more humid climate,, they did go up in weight after a few months but settled in,, they may be more resistant to moisture as stated,, back then I did not know how to induce the reflex using the least amount of sinew,, so the performance is average,,, I have some osage bows that have seemed to go up in weight, but maybe I am just getting older
I live in new mexico now so making a sinew bow is much easier in the dry climate,, I am working on a bow with long leg sinew from elk, and it was pretty fresh and easy to process and went on very smooth,,the easiest I have ever had,, so there has to be some difference in fresh and old,, but I dont have a clue which one would preform the best,,