Most of the records we hold at The National Archives were either created or collected by central government or the legal system, and at some point were actual working documents. This means that the people who used them had to have some means of finding what they needed, so they may have created their own indexes. Sometimes an index is part of the document itself, in a set of pages at the back of a book, and somtimes it is in a separate volume altogether. In this case the index will appear in the Catalogue as a separate document, and one index volume might also cover several record volumes. So that's why you often need to look at one document to identify the volume that contains the record you want in another, and to find the exact entry once you get there.
This can come as a shock to people who are venturing into archive research for the first time after using online indexes and digitised records. I'm sure that some of them think it's just an evil plot by archivists to confound the public. And while it is a bit of a nuisance, working your way through a system like this does have the advantage of helping you understand how the records were created.
|IR 27/153 (image from findmypast.co.uk)|
One of my favourite record series that you have to search this way is Death Duty Registers. These are 19th century records (more or less - the actual time span is 1796-1903) that record the tax collected by the Inland Revenue on the estates of the deceased. They are well worth the extra effort required to access them, because they tell you something of what actually happened to a person's money, which might not be exactly as suggested by the will itself. The records are in one record series (IR 26) and the indexes are in the following one (IR 27).
'Indexes' of this kind are not usually in strict alphabetical order, and when you think about it, that's not really surprising. They were created at the same time as the records, before computers, and the best way to understand them is to think of the way we used to keep paper address books. There is a page or section for each letter of the alphabet, and the entries are added as they occur. Death Duty Register indexes are annual, and the Inland Revenue, like some other departments, refined the system into 'cuts' as in the illustration, so that they didn't have to look through very long lists. Each entry then has a reference that will help locate the full entry in another book. There are fewer records of this kind than there used to be, because some records have been re-indexed from the original source, and sometimes digitised too, so you don't have to go the long way round any more. But there are still plenty left like this, so for the foreseeable future we still have to use the two-stage process of looking at a contemporary index first.
If you really want to know more about Death Duty records there is a research guide on the subject.