Most just changed the rules recently to eliminate expiration and yet each has specific conditions to keep miles intact and UNexpired!

Club memberships are also available in general at many carriers even for lifetime memberships, but the lifetime of the airline and changes in rules are frequent flier program rules are seemingly neverending!

Currently both NWA and DL are "realigning/improving" their FF programs!

As a result it is getting tougher to upgrade!

So it's increasingly VERY tough to plan too far ahead in this game!