Some sellers show the holo card that’s in the pack like this (since that’s also the only way to check if it’s a 1st or unlimited edition pack):
But with the Pokémon Web packs you can actually see which holo card is in the pack based on the barcode on the blue insert card. All packs will have a code in the form of 4521329 0ABCD X. The 4521329 is always the same and means the product is a Pokémon Web booster pack. The X is a random digit that’s irrelevant. But the ABCD part of the code is important, and indicates which holofoil card it will contain:
So I’m on the lookout for both a 1st and unlimited edition Pokémon Web booster pack where this ABCD part is 1309, 1310, 1311, or 1312. 
Note that we’re not 100% sure if these codes are correct in all cases, but it seems to be correct for all Pokémon Web booster packs that @melchior and @majomaal have seen thus far, whom are both aware of these codes. They first told me about it in this thread. Based on pictures of Pokémon Web booster packs I’ve seen since (while I was on the lookout for the Moltres), the theory thus far seems to hold true.
Greetz,
Quuador