I’ve seen that before - feels a bit rough… not exactly smooth like it should be.
Well - If it were me, I would use them, here’s why…
After firing the oven several times, those pits are going to fill w/ wood ash - and over time, the wood ash from multiple firings, along w/ moisture is going to fill those pits and the ash is going to get rock hard / smooth - like concrete.
I would say it’s a non-issue, but that’s me. Just a head’s-up, if you take them back to the store for replacements - odds are, all of the replacements are going to look the same since they most likely will come from the same pallet of the firebrick in question (the average landscape supply dealer will go through a pallet of firebrick a year - maybe 2 pallets. They are not a fast mover in the landscape industry).