Can Approved and Exported Invoices be deleted and how to detect deletion?

We have several invoices that were fetched via the Candis API and saved to our app, but comparing the list of invoices in the app and in Candis later on, we noticed, they are no longer in the Candis Archive List. The CandisArchiveUrl, which is parte of the response of list invoices endpint, does not resolve in the browser of these deleted invoices.

Could you please give us information about whether archived invoices can be deleted by the Candis user (my understanding was that this is not possible) and if it is, how can we detect it, so we can reflect it in our app's database?