It will be very interesting to learn more about the tomb’s contents and occupant once the chamber is opened and carefully documented (that occasion will be newsworthy). As I mention in our book Palenque: Eternal City of the Maya, there’s some circumstantial evidence that it dates to the middle years of the dynastic history, not quite so early as some have said. I believe Merle also thought such date a date, in the sixth century, was also most likely. The painted figures on the walls of the tomb are in a very curious and unusual style, but iconographically they are very similar to the ancestors depicted in stucco relief in the far more famous tomb of K’inich Janab Pakal.
A few on-line resources on the Temple XX tomb, long available: