We just bought the new holiday one at Epcot and asked exactly what "length of stay" meant (since we're local and will be visiting with family over the next couple weeks as they visit). They told us it basically just meant "until they change the design" since they don't give you a receipt or track your stay/dates in any way. So I'd say since they're all holiday now, that an older one wouldn't be honored, just as the holiday ones won't likely be much into January.