Thank you all who replied.
I have come to the conclusion that what we all read as 27th of September 1806, is actually
Writing the Will commenced on the 1st of September and was either not finished or signed
on that day, and the following day the writer inserted a "2 &" in front of
the 1, as there was no room behind.
I have seen Wills with dates in the past, but normally at the beginning, and another at
the end, when it was signed and witnessed.
Simon was the only one who picked that the Grant of Probate was dated the September 11th
David John of Esgerwen, Llansawel was buried on the 7th September 1806, and I am confident
he is the same person, and probably died on the 5th or 6th September.
2 & 1 is therefore the only Date that makes sense.