Thanks @puzzlezaddict although a disappointing answer for us :-(
We have been sharing the main game between 2 family members for some time and today purchased an expansion pack on my wife's account as she had enough credit. Now my daughter finds she cannot access the updates so is quite upset. They really should warn on this as most content is shareable as long as the same home console is in use.
XBox Help not helpful as states under 'What can you share'. Maybe the 'special edition' is the catch but would have been nice if they warned.
Share these with anyone who signs in to your home Xbox:- Games and downloadable content from the Microsoft Store
- Games from an Xbox Game Pass subscription
Account-specific items can't always be shared. Some examples are:- Game-specific content like Minecraft Skin Mashups or Halo REQ Packs purchased with in-game currencies
- In-game currency such as Minecraft Coins
- Certain pre-order bonuses and special edition content that can only be redeemed once