In my experience, you can request a VAT form and have everything filled out except the PP#. You can fill that in once back on board. Whether or not they are "supposed" to look at your PP, I don't know. Having shopped at several different stores in different countries, I've never had a problem getting a VAT form without a PP. They just leave that line blank. Now watch, on my next trip someone will insist. You could also take a photo of it with your phone to avoid carrying a hard copy.