Unless you know the hours on a drive, you might get brand new ones, or you might get ones with 50k hours on them. They may also be from the same batch, which isn't ideal for data durability.

If it helps, my strategy is to use RAID6 to handle up to 2 drive failures, and apart from the initial 4 drives needed to initially create the array, I just add another when I need more space. Then even if I get drives with sequential serial numbers, they're going to have differing amount of life used.

Also, always keep a couple spare drives for quick swapping. Especially with RAID6 given how long rebuilding the array can take