"The earliest markings date from nomadic times AND tend to be on prominent outcrops"
The only way we have of dating RA at the moment is by association and the earliest in the UK is found inside passage graves and funerary monuments . Although the prominent outcrops may be older we just have no way of knowing that.
" (very few burials are found round rock art panels)." Very few panels have been excavated , but when they have they do not have burials .Although see above . One certain association RA has is with burials and death .