Item Numbers for Steam releases?

[vigorousjammer]

I was reading the style guide, and it says the item number MUST be from the manufacturer, and can't be taken from other websites.

However, I'm wondering... Steam games all have a store page with a specific unique number in the URL... for example:

http://store.steampowered.com/app/238210/

or

http://store.steampowered.com/app/17500/

I've only seen them in 5-digit and 6-digit varieties, but every number is definitely unique.

My question is... seeing how Steam is somewhat a manufacturer (Or at least as much as you can be in terms of digital downloads), should we use these numbers as item numbers, or should we limit that stuff specifically to actual retail releases?

[foxhack]

We don't add these numbers. There's no point, because Steam changes these numbers for older games whenever they please, for no reason, OR hides the numbers from public viewing when an item is removed from the store, regionally restricted, or an item is tossed into a bundle when it had its own store page for years (see the RIP games.) The former breaks an item's news feed, making it pretty difficult to find the item's actual release date sometimes. The latter makes Steam redirect you to the front page or tell you "blah blah your country sucks so you can't buy this game."