Omission of vowels

I understand the principle that  vowels which are scarcely pronounced or are pronounced as schwas may be omitted from shorthand outlines; but I find that in some dictionary outlines such unimportant vowels are included, whereas in other dictionary outlines phonetically important vowels are omitted.
In Anniversary, for example, the E in the word "camera," seldom pronounced at all, is written, but in the word "patron" the A, the principal vowel in an accented syllable, is omitted.
Inclusion of the E does not make "camera" easier to write, nor does omission of the A make "patron" easier to write. 

(by Bruce E. for group greggshorthand)