A Thorny Dilemma

Two actinic traps were out in light rain last night - it was dry when I set them up and Derek Brockway's bulletin yesterday lunchtime said that night would be dry!  So I'm blaming him for the very meagre turn-out, only 10 moths of 7 species were recorded.  However, they did include another Lunar Thorn, hence the dilemma: is this another case of London Bus Syndrome or has the same moth appeared twice?  Firstly I should say that when Wednesday night's moth was released I was fairly sure that it was taken by a bat, which swooped down very close to me and followed the moth in flight.  To put the matter beyond doubt I was hoping to detect pattern/shape differences , and have been studying the photographic evidence:

In both pairs of photos the moth on the left is Wednesday night's, the one on the right is last night's. There's little doubt in my mind that both moths are very similar indeed in their shape, pattern of markings and colour, being very pale examples.  Is this very surprising though?  It's clearly not a very common species here, so it's likely that two individuals caught locally would be from the same brood and therefore genetically similar.  Any observations and comments would be welcome!