Is there any lore justification for being able to do previous expansion's sidequests?

[Dikatis]

Although I definetely agree with you and share your opinon, unfortunately the development team lately has increasingly pushed lore explanations for various gameplay functions, even when there was no real need to do so! (Such as Fantasia and ability telegraphs/AoEs). I guess a line has to be drawn at some point as to where lore ends and "it's just a gameplay function and nothing more" begins.

Fantasia being a shady potion that costs a fortune and only a handful of people know about doesn't require that much of an explanation? And ability telegraphs being "read your opponent's body language to anticipate their attacks" as seen in the Hall of the Novice since Heavensward isn't really much of a gripe?

But Brightamethyst has the right of it. Sidequests take place in the expansion they were created for. You're just reading a book out of order.