In order for me to properly assess what you have I will need to see images and clear, in-focus close-ups of the marks.
If you had already attached images to your initial posting, they are not showing for me here on my end.
Please send the photos at your convenience. There is not an extra charge to provide more pictures here.
Thank you for the images. Please allow me some time to look these over for you.
There are 3 images attached that I can see here on my end - 2 of the obscured stamp and one of side of pot showing lizard tail end. Is it possible to capture a more in-focus image of those impressed letters as well as the underglaze blue stamp and the diamond mark. Ultimately, the diamond mark, if impressed well can establish the day, month and year this was made.
The R in diamond mark is a British Registry diamond, and that will help date this; it is not a maker mark. If you can please include a very clear, in-focus image of the R diamond stamp to start, that will be very helpful.