I think the key question here is "after break in"? If a bow is weighed along the tillereing process and one gets to the weight they want,they shoot it a while and then finish it. It ain't broke in, so yes it can loose weight.
A dry wood,well tillered,shoot in bow,(before finish) should stay close to original,even after much shooting,(after finish). Long brace times come into play here.I suppose if a bow was braced for a year(exagerations here) it would lose integrity,therefore losing weight.
Many variable to consider,but as for an answer to the question, then I would have to agree with Art and Gordon on this one.
The key in my mind is shooting the unfinished bow along in the process,whether @ 20" or 22" etc. I have learned to brace my bows and sweat them for long periods of time as I am working the wood off, gaining ground on intended weight.This of course helps the wood to attain a new memory, and allows the wood to respond to removal. (sometimes we get impatient),So there are fewer surprises.
Just my two pennys.