All of them. The more coins have been mined, the fewer are left to mine and the harder they are to mine.

It's guaranteed scarcity. By design. All you have to add to that formula is the idea that there's a demand. And that's what every ICO is: hype about demand for a decreasingly available thing.

Once you have been sold that there's a demand, the appreciation is guaranteed by definition of what it is.

Seeing as most ICO are ERC20 tokens on the Ethereum chain you are most certainly incorrect about your deflationary theory implying appreciation. Since most ERC20 tokens are 100% premined and sold during the ICO, there is no concept of "mining" with those ICOs (except maybe Minereum :p ).

Please avoid making generalized statements, especially ones that are flat out wrong.

If they’re “pre-mined” then surely there is already a preset limited amount of tokens?

wouldn't that apply to every trading card and collectible item then?

Usually the companies that make trading cards can also print more.

Not generally, because there's no promise of any future utility or increase in demand, at least by the manufacturer. People buy them because they hope they'll appreciate in value, but that just makes them the subject of speculation, not a security.

There are, but many of the ICOs are controlled by a company that reserve the right to change the contract at any time.

Can you point to a specific ICO where the token contract allows for additional token issuance? The ERC20 reference code does not include functionality for this, nor for replacing the token code at a later date.

They don't advertise that because their lawyers told them not to. There are lots of ways to dance around this and imply appreciation without stating it.