Endnotes are the worst. Footnotes all the way.
Well, the problem is, the endnotes are quite detailed, and sometimes a page or more long in themselves. They provide the actual historical setting for whichever battle Flashman is engaged in (Charge of the Light Brigade, Indian Mutiny etc). Sometimes Flashman refers to a particular event or scandal that everyone who lived through that time would and should know about. The thing is, the books are presented as his secret diary.
There are usually 2 or 3 quite long appendices giving an actual history lesson about the major incident and/or key historical characters referenced. The numbered notes refer to remarks made by Flashman about some historical trivia or moment of the time.
It does take some getting used to. You do wind up reading the books with another bookmark in the endnotes so you can flick back and forth easily. If you haven't read them, at least give the books a go - if you like historical novels with a lot of humour, they are great. And you wind up with a terrific history lesson, as well.