The notes say that vam translates as 'this/that' (singular) and velth translates as these/those (plural).
No, that's not what the notes say.
"This, these" and "that, those" uses noun suffixes: -vam and -vetlh, respectively: Ha'DIbaHvam "this animal", Ha'DIbaHmeyvetlh "those animals".
Whether "this" or "these" is appropriate as a translation of -vam depends on whether the noun is singular or plural; similarly with "that" or "those" for -vetlh.
So -vam is for "this" or "these" (close things), and -vetlh is for "that" or "those" (far things). Nothing to do with how many things there are.
Do you have a suggestion for a more understandable wording?