postscript vs notation

postscript and notation both are nouns.

Word	Noun	Adjective	Verb	Adverb
postscript	Yes	No	No	No
notation	Yes	No	No	No

As nouns, notation is a hypernym of postscript; that is, notation is a word with a broader meaning than postscript:

Other hypernyms of postscript include annotation, note.

postscript (noun)	notation (noun)
a note appended to a letter after the signature	the activity of representing something by a special system of marks or characters
textual matter that is added onto a publication; usually at the end	a technical system of symbols used to represent special things
	a comment or instruction (usually added)