One of the biggest challenges inherent in archival historical research is figuring out how records or documents are organized.
Sometimes you have to backtrack to find a permit or registration number from one set of records to get into another set of records to find the information you’re really interested in.
A cardinal rule of archival arrangement is that records are kept in the order in which they were created. That’s because documents found next to one another can give clues about the way different records were created or used, and about the reality of life at the time. It also explains the rationale for some of the custodial work of archivists and the instructions you are often given to use a set of documents. It’s essential they remain in the order in which they were found – or given to you to use.

It’s part of what makes archival research challenging but, in my opinion, also interesting because it gives a portal into the thinking of a past era.
While doing your research, it may not be apparent how a set of files or documents are arranged. This might be explained in material accompanying a set of documents, probably written by the archivist who processed the records.
But in many cases – mostly to do with time and budgetary priorities – you’ll be on your own to work out the system in which the records have been arranged. You’ll have to look at them with a critical eye to figure out the system that exists, so you can use the records most effectively.
Think of it as an adventure! Because otherwise you could become very frustrated.