System should avoid advertising already owned content...

The system is already set up that way. If your settings allow it you can purchase paid for M rated content. You just can't download free demos and trailers because they are considered advertising.

@moonpoco

Actually, in the US, "forever" has a legal meaning when it is used in advertising. When the word "Forever" is used in a contract or sales agreement (ie the advertising at the point of digital purchase) at the point of purchase) means "perpetual and unending."
So it is not just a t the end of the hardware lifecycle that a purchaser would retain ownership, it would be unending, and they would/should have the ability top access it as long as the purchaser can maintain the current medium (the hardware).

The big word in the advertising at the point of purchase is "own" though. "Own" definitely has a legal meaning. When you "own" something you "have legal title or right to something. Mere possession is not ownership." The very fact that MS streams the content
through the Xbox Fitness app makes the statements made at the point of purchase fraudulent, especially if you weren't savvy to MS' app streaming (many thought that when they purchased the content the download was the actual program instead of an unlock to
stream, which the advertising implies).

So basically, a customer was told that if they purchased the content, they would receive perpetual, legal right to the content. MS' plans of "sunsetting" the app and handling the content in such a manner clearly violates what they advertised (or contracted)
at the point of purchase.

When we purchased these programs, they were advertised with
"You can use this app now or buy it to own forever." directly next to the button to purchase the content. The advertising clearly states that the content we purchased is ours to "own," not to just be able to stream it until MS sees fit to sunset the service
and disable any and all access to the content that paying customers "own forever." Anything less than full refunds or making the content accessible without the Xbox Fitness app is paramount to false advertising, and should be pursued by consumer protection
agencies.

On another note, because of this I am certain that an "all digital" future with Xbox/MS in not for me. MS is simply just showing they are not trustworthy enough with digital content, especially with their notion that it does not depreciate the same as it does
with the retail market. I personally have decided to never again purchase digital content from MS (Xbox or Win10) and have recently canceled my gold subscription since I used it for DwG and GwG instead of multiplayer.

After another thought, if you go to xbox.com and log in with one of the accounts, then browse the store you should be able to see if the content has already been purchased which should mean that account owns the content.

If a game is deleted you should be able to re-download the title providing the owning account does it or it is set tot heir home console.

here is a question why doesnt he just buy his own content with hisown correct regional account

it is recomended thst you should have an account in your actual region and it is in that sticky I posted to avoid issues with region errors and downloading