I'd probably use a report workbook with queries on hidden pages.
1st query gets PropertyID's plus any other data you need from both spreadsheets where PropertyID in both of them is present, and any of other fields was different, plus comment field composed;
2nd query gets PropertyID's plus any other data from 1st spreadsheet where PropertyID in second one was missing, plus additional comment field;
3nd query gets PropertyID's plus any other data from 2nd spreadsheet where PropertyID in first one was missing, plus additional Comment field.

NB! All 3 queries must return the same number of fields!

Now you create a report sheet, with uses UNION query to read info form 3 hidden ones, ordered by PropertiID.