1975 opening / X3 opening

Wasn't the opening to X3 set 20y before X3 (so maybe 1990 as X3 set slightly in the future around 2010 or even 1986 if you say X3 happened the same year of release but then all 3 Xmen movies were set in the not too distant future probably like 5 years ahead so X1 set 2004 or thereabout) and Jean is about same age as in the opening to Dark Phoenix (1975) ???

I don't understand

I guess if they hadn't put 20years earlier in X3 it'd have worked ok as then it could've been around 1975 as well (and Charles still using hanks drug that hanks mustve perfected so he's walking and using his powers - also see the end of Origins: Wolverine set in 1979 - 6 years after DOFP 1973 so Hank could easily have perfected the serum so Charles uses it from time to time)

its pretty much the one thing that dosnt work in the chorology of the 2 timelines as everything else you can sort of explain (even Charles walking at end of Origins/start of X3 as above, and Logans whole origin in becoming Wolverine - Vietnam War/Stryker/WeaponX etc it all works out but slightly different in both timelines from 73)