The official Excel VBA documention on the CommentsThreaded collection lists all the methods (Item()) as well as all the properties (Application, Count, Creator, and Parent) -- which all apply to the Collection as a whole. An individual element of that Collection would be a CommentThreaded object, with methods (AddReply(), Delete(), Next(), Previous(), and Text()) and properties (Application, Author, Creator, Date, Parent, and Replies).

When using OLE from Perl, you just have to change the syntax from the MS documentation showing VBA syntax, and use the equivalent syntax in Perl, for referencing elements of arrays or for calling a method or accessing a property on an object. I don't have Excel available anymore to test, but I believe it's just the simple $comment->AddReply("Current sales") (similar to the AddReply() example) or $comment->{Date} to get the Date of the particular $comment.

But the MS documentation for the Excel VBA interface is where you go to find all the methods and properties for any given object, even though you're using Perl instead of VBA.