The word is to wait a year to let the waxy outer layer of the straw wither away, letting the plaster
get stuck better.
As for moisture content, the farmer won't bale it wet, or it would go bad for him. Work wasted. Our neighbour just waits a bit longer
if it gets rained upon to let it dry out again before baling.
He says he prefers that straw, since it sucks up the piss of the pigs better.
Weight I feel is difficult to use for a moisture estimate.
Some bales were heavier than others when we built our house. When looking at the structure of the bales these just had finer straws.
/Peter