Nothing printed on the glass
At the supplier this site links, vials ship unlabeled by design, and no lot is printed on the vial. That is a stated practice, not a lapse. It also means the reader cannot read a lot number, a batch code or a date off the glass, because none of those is printed there to read.
This site records the practice and stops. It does not read anything off a vial, because there is nothing on the vial to read, and inventing one would be exactly the kind of unsourced claim it flags in other people's copy.
Why a pair raises the stakes
An unlabeled vial holding a pair looks exactly like an unlabeled vial holding one compound. There is nothing on the glass to distinguish two identities from one, so the whole question of what is inside moves off the vial and onto the document.
For a single-compound product a reader is asking one question of the glass and getting no answer. For a two-component product they are asking two questions of the same blank glass and getting the same no answer, twice. The gap does not double in size. The number of things it hides does.
The label you can actually read
Since the glass says nothing, the label that carries information is the certificate. That document is where identity is resolved, per component for a pair, and it is the only surface in the transaction that names what the vial cannot.
The certificates from the supplier this site links are published on its certificates page, and this site links that page rather than describing a file it did not open. See its certificates page, or read what a two-name document has to prove at the document that names what is inside.
The published route back
A blank vial still needs a way back to its record, and the supplier this site links publishes one: message support with the order number, and the order is the thread that ties a shipment to a certificate in place of a printed label. It is a stated route, and this site reports it as stated.
For the full account of what that supplier publishes, including where it publishes nothing, read the published route back to a certificate.