Keep the relevant civil evidence and actual dates separate from reservations, announcements and intended events. Submit the material required by the official process. Separate the documents by the date of the event each one records. A civil marriage record proves a status from the day it takes effect; a venue contract, an invitation and a savings transfer prove intentions held on the day they were made. Both may be true, and only the first answers the question asked.
Do not turn an intention into a completed fact
A planned ceremony is not evidence that the legal relationship already exists. If the relationship changes, preserve the real chronology and follow the applicable instructions rather than backdating the application history. Build a single chronology and leave every document in the position its own date gives it.
Where the relationship changes during the process, that chronology is what allows the change to be explained without recasting anything earlier: the original answer was correct when given, and a later event is a later event. Ask what the official instructions require to be reported, to whom and within what period, then keep the acknowledgment with the file. Amending a record afterwards is a documented act with a date of its own, and it reads very differently from an original entry quietly altered to match how things turned out.
Date every note you make as well.