What is an "external sheet"?
And multliple comments will only show if they are (a) from the same user and (b) made without moving away from this one page.
(b) can be overcome by using cookies or local storage.
But (a) can be overcome ONLY by using server-side coding and storing the comments to a file or (much better) a database.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.