it seems that it worked as intended, thus they have a QA process. The problem was in the wrong IDs provided and I doubt that at their scale they have a staging environment that duplicates the customer data.
If there is no feasible way of replicating their production environment somewhere else, then there should be some sanity checks in place. Something like "if an abnormally high amount of customer sites go down during the script's execution, kill the script". This is a 20/20 hindsight approach though and if Atlassian engineers can't solve I doubt a random HN user like me can.
I'm not looking to help their specific problems, but this is more from a general question I've thought of doing but never have done just because I'm sure I'd get laughed at for blazing my own trail
WHENEVER a human is involved in the chain, UUIDs can be suspicious because there's no easy way to verify what it is, whereas a human has a good chance of realizing that $1,342.34 is probably not a valid date.
This might be customer id and customer name, article number and article description, invoice id and invoice number etc.
Then it is usually very clear to the recipient what they've been handed.
Also, for internal autoinc-type id's, we mostly use sequence generators with non-overlapping "series". That is, we'll start first one at 1 million, second at 2 million or similar. Not perfect but can be useful.