The double booster pack deal only applies if you buy the packs while it is active.
In simple terms, this means that if you bought the boosters when the deal is on you would get twice that you would get without a deal (eg you bought 5 and got 10).
Other than that the "deal" remains the same but only the quantity of the booster packs you get changes

The double booster pack deal only applies if you buy the packs while it is active. In simple terms, this means that if you bought the boosters when the deal is on you would get twice that you would get without a deal (eg you bought 5 and got 10). Other than that the "deal" remains the same but only the quantity of the booster packs you get changes