Since my last posting, Hyatt staff have responded three more times. I have learnt that they will only accept screenshots in pdf or jpg format, and the screenshots have to show every stay from 2015 including check-in and check-out dates. There must also be an account overview screenshot showing full name, Starwood status and total stay count. For me, that amounts to four screenshots which I put in a pdf document as instructed.

Now, they say they can open the pdf document, but can see only my login page screenshot, which makes no sense. I will try sending each screenshot as a separate pdf document...