I have two aromatherapy books (both for slightly more advanced practitioners) that do NOT feel it necessary to expound on the history of scents and the various methods of getting the essential oil out of the plants and into the bottles. The other twenty or so? Even the ones supposedly for not-QUITE-beginners-anymore? Right. At least a chapter each on
a) what is an EO
b) why EOs are hard to get at including where they are in the plant
c) where EOs come from (regions, etc)
d) history of EOs and perfumes.
And all list the same sources for their information; in many cases it's darn near C/P from one book to another.
One book drives me batty all by itself -- in each and EVERY recipe, the directions include :"Place the carrier oils in a clean container, add the essential oils, and gently turn the container upside down several times or roll between your hands to blend. Apply as needed." (Aaaugh, wait, she forgot to tell me to put the lid on! i just dumped the oil all over the floor!) If the author had put that at the beginning of the chapter and said "this applies to every rx unless stated otherwise" it would have resulted in a 20% savings on paper, ink, and transport costs.
I suppose that the repetition between books is "just in case" a person only GETS one book, so they'll have the info, but when you have several it wastes time and shelf-space! Hello, posty-notes!