When did users start tipping off mods about games(cv)?

probably the moment people started abusing things.

to note, games that are just added to library for free won't get 0'd out as they cannot be abused. This was more common in the past and anything from steam itself is just add to library.

About your GTA4 keys, gotta see them like this. The key doesn't activate an app. It activates a sub. Each key will activate a different sub. But when devs merged the games, they changed the subs so they contain the same item(s). Which in this case is GTA4 The Complete Edition: https://store.steampowered.com/app/12210/Grand_Theft_Auto_IV_The_Complete_Edition/

You can check it for example in this package: https://steamdb.info/sub/4152/apps/
The name is Episodes From Liberty City, but the app it contains is GTA4 complete. I hope this makes things clear for you.

You must have some enemies. They do the same thing with me. I used to buy a bunch of keys to give out to be nice but some people would report it and cv would be removed and backdated to right before I did giveaways despite me being able to spend a few minutes and seeing deeper discounts on those games months or even years earlier. Now I just kind of lurk and do a giveaway now and then if I can afford it. Just seems silly to spend money on keys for them to wind up giving 0 cv because some internet tough guy doesn't like me.
I wouldn't worry too much on it.

I reported multiple games or even full bundles where I found out the games I've been giving away were unbundled, despite clearly coming out of a bundle. Support can't be everywhere, and I'm not an exception from the rule. (Also easier to calculate with numbers if you already know that something is bundled, rather than going for too high discounts, and then the game ends up on the 0CV list)

It sounds kinda nefarious the way it's presented, lol.

Many games I give get reduced or zeroed. That's the nature of it. Just give more!

Some I wonder about like Mass Effect Legendary Edition as Reduced CV.

I do think there should be an eventual amnesty window on Reduced/No CV games. Like if the market price on gray sites rises enough after years, mark it back to Reduced/Full.

If report games when i create a GA and see the game is wrongly listed or when i buy a game for -95% and see it isn't listed as "bundled" or buy a bundle with -99% and see the games aren't set to "free".

Only in very few cases i have energy, time and motivation for deeper checks and with them i try to hit the notorious abusers/exploiters that give hundreds, or in many cases, thousands of freebies that aren't listed correctly, to get, unjustified, cv.
(Always the same, few dozen, users since years. It would be easier to perma suspend such abusers/hardcore exploiters instead to try to fix each games cv that they exploit)

Some mods (who come and go) were very active on it a few months ago, and there was a big influx on devs that abused their games.
Valve purged many (but not everything) and steamgifts added a lot to the list.

These people were hallway monitors in grade school and now they have time to fill.

In before suspension for picking up on inconsistencies which aren't equally applied.