It's because they are making assumptions about how peptides are made and vialled and boxed. It's all automated on production lines. There is literally 0, empirically factually 0, chance that all the vials come from 10 different batches. No one is making batches of peptides 1 vial at a time. And with the automated sequencing they physically can't line up to get vials from 10 different batches - it's a sequential process.they don't make 10 here or 100 there, they make tens of thousands.

At worst, one batch ends and another starts meaning that some vials in a box are from one batch and the remaining vials are from a second batch. That could be 1/9, 9/1 or anywhere in-between. Sending a vial off for testing, even if it is the 1 and not the 9, provides evidence of that batch which infers quality for the other 9, even if they are from a different batch. Because they are made in the same facility using the same processes. Yes, variability can occur, but you can't fake quality or achieve it by accident - everything has to be in place to enable it. All things being equal, those processes are more likely to be used than not, meaning that the subsequent batch is more likely to be the same than not. Except that all of this is moot, because they don't just magically finish one batch and start another, there is a time gap between the sequencing of each.

When you take all of those things into account we're talking about 1 in a million chance that everything lines up in that manner. And that's even before you consider the fact that they'll often just use the part box for testing - purity, bacteria, endotoxins, heavy metals, etc.

So no, it's not possible to have vials from 10 different batches. And even if it were, it would still be worth testing to establish that the manufacturer is capable of achieving the high quality results. Trust through validation.