It's generally dried before smoked, or for food products the oil is extracted. I would think the oils would eventually evaporate from the dried or the extract but I don't actually know. It's legal here in WA and the packaging I've seen doesn't have any dates on it so take that with a grain of salt with the supply problems we've had (the state limited the amount produced, so for the first year at least there were reported shortage; they heavily misjudged demand :)).

I'd think it's very similar to tobacco. Vape for tobacco doesn't really expire, it's just the niccotine. And cigs keep for a long time. They get brittle over time, as do cigars, so I would think it's very similar. Again I'm not an expert, I just live in a state where it's common.