But what visual clue do you look at when reading the page that indicates to you that it's the same as the previous page? how can you tell the difference between "new data" that is "the same" as the data that was on the previous page, and "old data" that really is just a repeat of the data you've already seen?

If you, as a human, can't do that -- then there's no way your code will be able to. ... But it sounds like you've already found your answer. you can tell if the page you are looking at is the same by looking at the PRODUCTID of each row, and if there is a duplicate (or all duplicate) from the last page, then it's hte same page.