How good is your math

Zero, because you should submit a delete giveaway request ;)

Lol after reroll it's 100% assuming you are giving it to someone doesn't own the base game or the DLC and the guy you rerolled was the one who owned both. So you would only need 1.

Now if you had no intention of giving the DLC to someone who already owns it or doesn't have the base game in which case there is 0 % chance of finding one since there is no eligible winners. So you could reroll another 15 times but still end up doomed. I am assuming that rerolling takes them out of possible winners. I have no idea if tat's actually how it works.

math? what kind of food is it?

Hmm, usually if users don't have the base game, they cannot enter. However, some games(ex: Rome Total War - Alexander) allow to enter. I had to re-roll once such a case.
Anyway, about your question, there is no way to find the winner, I think. After 15 re-rolls, and finally you will need to delete the GA. :(

Talos - serious DLC?

My math? It doesn't even exist.

As it's stated 0% & you'll never find a winner because of the 16, 1 already has the game & DLC & 15 don't have the base game.

∞ rerolls required

This is me doing math ofc

But honestly everyone should watch this even if they don't understand

Unknown variable exists as any of the entrants that didn't have the base game could end up buying the base game in the time it takes for a reroll request to be fulfilled.

None of the answer, You have 1/16 chance to have to do a reroll, unless winning entry got the game meanwhile or doesn't want it.