As far as I understand, you mean there are notes in the arrangement which are not part of the MELODY.
In fact the notes you circled ARE in the sheet.
Each simple chord (triad) consists of 3 notes. So it's absolutely possible to add ANY of the three notes from that chord. There will be no disagreement. Your sheet says G is played in measure 9 - which means it's safe to play (add) any of the 3 notes from chord G. This implies harmony (2 or more notes played simultaneously implies harmony or lack of it). In all of your sheet the added notes do not contradict the underlying chord at any moment, so in terms of harmony there is no contradiction.
Tip: it helps to learn how chords are created. Simple triads. Then more complex chords, etc. If you learn how to understand sheet (not just tab) your understanding of theory will improve.