I'm not privy to the ins and out of it, but there is a mechanism by which they can match them up, and is the reason why you can reuse your old PS without getting flagged for plagiarism.
I m not sure how they did it, but my track number from 2013 and my one for 2015 ending up being the same so they were somehow linked after sending off my application even though many of my personal details had changed since.
I m not sure how they did it, but my track number from 2013 and my one for 2015 ending up being the same so they were somehow linked after sending off my application even though many of my personal details had changed since.