I really hate to say it but this needs to be switched off before the photos have been taken. After that, they are electronically printed on so the only way to remove them is to crop them via photo editing or retake them.
I have the same problem on 700 photos I took in Italy on my first venture with the HX9V. The date stamp must have been turned on, but it doesn't display onscreen on the camera on any of the photos, so I didn't know. When I transferred them, the date stamp showed up on the images. When I check on the camera, even in zoom view mode, the date is not there. How can I salvage my work without editing? How is it that they display correctly (no date stamp) on the back of the camera? Thanks for any help you can provide.