@Anonymous - I just thought of something else, too, I think:
Let's say you've got 10 rows in your spreadsheet....If we use a condition to 'sync' things, it will play out like this, right:
When the Flow runs, it looks at the first task and asks "Is this in the spreadsheet?"
If it is in there, but let's say 4 rows down, it's going to get a "No" response 3 times before it hits the yes. And in each of those 3, it will add a new row. Then, it will find the match, but keep going. Each time, not finding a match, and each time adding a new row.
When it hits the 11th row, it will match again, and update that row, and then carry on until row 19. Each run will add more and more rows (exponentially?) and this will get ugly fast.
I don't know what the fix is (To-Do?) but I'm sure one of the experts have already thought this through. Let me know if that's something you've already addressed...but I didn't even think of it until I started building my own. 
-Ed-
If this reply has answered your question or resolved your challenge, please consider marking it as a Solution. This helps other users find it more easily via search.