Research question
What is a lot number on a GetReta vial?
A lot number is the batch identity printed on the vial. Every vial from that filling shares the analytical record: HPLC purity, mass-spec identity, test date and the labelled compound. It is not an order number. Your checkout reference, which looks like GR- followed by letters, is the sales record. The lot is the laboratory record.
GetReta prints the lot on the vial and repeats it on the certificate in the carton. The public lookup at /coa sends you to /lot/ and that code. An unknown code returns a short message and the email orders@getreta.co.uk. The row GR-SAMPLE-0001 is marked as a sample so the page can be demonstrated. It is not evidence for a vial you were sent.
Photograph the label if the code is partly rubbed. Do not invent missing characters. A near match is still a non-match. Research use only.