Have you actually bought the certificate? Or are you going just from the index? I once bought a certificate were the index said that the regiment were the 17th Lancers, and it turned out to be 17th Foot (Leicesters). Can you post an image of his occupation if you have the certificate.
The Leicesters did not become Royal until 1946. Could it say Royal Lancs and not Royal Leics?
Ken