Both my Royal Enfields (1938 Model A and my 2016 Classic Chrome 500) have hand painted pinstripes. You have to look closely to see the brush marks. Maybe they were done by this fella?
He's not that old, but who knows? I healthy diet and clean lifestyle supposedly do wonders for the seven signs of ageing...
If you have a read through my build blog you will see that I bought the tank for the 1938 in 2014, so he may have done it. http://2fiftycc.com/index.php?threads/1937-royal-enfield.2990/