https://www.flyertalk.com/forum/37243443-post1071.html Makes it clear that it was a year and not 20 months
the wording in the perk also makes it clear that if you have a membership already, the year is added rather than discarded. MP T&C are also explicit here
Alaska Lounge+ MembershipYou will receive a membership that allows you and your immediate family or up to two guests access when traveling with you. Membership duration is one year from your selection date. Existing Alaska Lounge or Lounge+ members will have their membership extended for any periods of overlap between their paid membership and their gifted membership. All Alaska Lounge+ membership terms and conditions apply. Visit our locations page for details. "Immediate family" is defined as your spouse or domestic partner and children (under 21 years of age).
https://www.alaskaair.com/content/mi...erks-selection