Please Allow 50's to Enter Ishgard w/o having completed MSQ

[Reynhart]

Well in XI's defense, each expansion had a different scenario. One quest I remember was tied to both RotZ and CoP was Apocalypse Nigh. In order to do that quest, you had to have beaten both those expansions because it drew conclusion to both expansions.

Actually, no...
RotZ was tied to FFXI vanilla, and you had to do the main quest until rank 5 to unlock it, BUT, RotZ is also the reason why you're allowed to enter Norg in the first place, yet, you could walk there freely to unlock NIN and SAM.
As for CoP, it's whole plot is started by the end of RotZ, they just don't mention it until very late in the story.