In the following sentence, 'The graph can be found in the appendix [preposition] this report', what is the correct preposition to use? In particular, is 'to' more appropriate than 'of'?
I wouldn't object to appendix for, appendix of, appendix behind, appendix following, and so on, but by the NGram, appendix to is favored by a wide margin:
There may be some false hits here as appendix can also refer to an internal organ, among other things, but since those uses would be overwhelmingly appendix of (e.g. The appendix of a ruminant, unlike the appendix of an ape, is a true appendix, or cecum), the point stands.
An appendix is something that has been appended to a document. Therefore, you would describe it as the appendix to the document.
The appendix does not belong to the document. Therefore describing it as the appendix of the document is incorrect.
An appendix is not part of the document. If it were, it would be a chapter or a section.