Julian Cope presents Head Heritage

The date won't matter in relation to the accuracy of an equinoctial alignment . At the latitude of say Vigo 42.19 with a level horizon the equinox will very close to 90 and 270 degrees . For different horizons this can vary but 257 degrees will not be aligned on the equinox . Even if it was aligned on the equinox you could find plenty of similar examples or any other astro for that matter ,the number of possible alignments found within a marked rock with 50 cups is immense .
.Iwouldn't associate your two categories with British rock art .Weapons are very rare in British rock art . George De Saulieu came up with couple of terms from French rock art studies that could be applicable here “art ostentatoire “ and “art discret “ .Possibly private and public .The large prominent erratic marked with a few to amny cups and rarely consistioing of too many complex motifs can be seen as public ,they are often close to track ,I dicovered a new one today http://www.themodernantiquarian.com/site/15141/connachan.html contrasts with much more difficult to find complex motifs that are often buried under turf or in extreme cases sealed in a monument . Half rings and cups associated with fissures are also found at the edge of rocks and can give the impression that what you are looking at is cup and rings but they are arcs that were never rings scroll to 8th pic http://www.themodernantiquarian.com/site/8872/glascorrie.html.
.IIFrom what I have heard there is a huge amount of Galician rock art waiting to be uncovered .