Kittylover Unless someone remembers having dug up those high value tiles and where they were dug up, then they aren't going to have them as a landmark anymore to refer to in order to find if you dug them up in the Hard Part or not.
Anyway, here is a screenshot. This is the last screen of Lugash Palace and Diggy is standing next to the entrance that leads to the Hard Part. I've circled the entrance in red. If you go through the entrance there is a signpost immediately on the other side which tells you it is the Hard Part, and there is always a signpost to warn you when you are going to be entering the Hard Part.
https://image.ibb.co/ioF76U/Lugash_Palace.jpg
