Finding unique data with a fully complete data set and a half co

So it sounds like you have a situation where you get the document today which will have some of today's data (but not all of it) and then tomorrow, you will get another spreadsheet which has SOME duplicates of what you have already received on day 1. So you use your day 2 spreadsheet, and you do a vlookup (on what field?) to compare which records you already have in your data.

So I would guess that your ask is to strip out the records you got on day 1 and leave only the latest values you got on day 2? Or would you rather keep day 1's values and delete any duplicates (but only the duplicates) on day 2? Or does it not matter which record (day 1 or day 2) because they are the same - you just need to ensure that you don't have duplicates?

Is there a field on your spreadsheet which allows you to pick up day 1 vs day 2?

It sounds to me very much like something that Power Query would handle very effectively! You can pull in both datasets, combine them , deduplicate them and then output the data to your spreadsheet.