OKW when it began in late 1991 had essentially a 50 year term to January 2042. That was then also the designated end date for VB, HH, BWV, VWL and BCV although those all opened in later years; thus none of those ever in fact had a 50 year term. SSR then became the first one to have an end date after 2042 and when it opened it had a 50 year term to January 2053, AKL likewise a 50 year term when it opened to 2057, and BLT to 2060. OKW had an offered extension to 2057 which some OKW owners took and some did not giving it two end dates.
If you own at BLT and are considering purchasing elsewhere but don't want the 2042 contracts, you are limited in your choices at WDW to AKL, SSR, or extended OKW (which itself is usually available only through Disney) and if considering those, they all have higher dues than BLT and are easy to get at the 7 month window (except AKL concierge or value) and thus it is not necessry to own at those to usually be able to get a reservation.