You are right - depending on the source, there is great variety in the list.
I have found out from Art:Images and Ideas that in 1899 an American artist
named Wesley Dow wanted a systematic way of teaching and learning visual
qualities. Thus, he invented the elements of art. This list has evolved and
changed with the times.
I use line, shape, form, color, value, texture and space as the elements and
using these we create balance, rhythm & movement, emphasis, pattern,
proportion, unity & variety. I use the elements and principles as my outline
for each semester.
Just my 5 cents worth. Martha