I've never stored LP gas for more than a year, year and a half. No problems but for all fuels fresh is best and using the older stock up is probably the best idea.
As for the butyl alcohol, I have no experience with it but most alcohols do store well. (Yeah, that kind too!)
LOL on the other alcohols comment. It's mostly the additives in conventional gasoline reacting that create issues.
Sometimes the conspiracy theorist in me wonders if this is something intentionally done to limit fuel storage life for whatever reason(s).