If we assume the paint is original, the bike could be no earlier than 1974 (which is when those 531 decals - the "Reynolds Tube Co. LTD" gold band decals - in english - were used for the first time.)
Those decals were only used in 1974, and 1975. After 1975, the Reynolds 531 brand was trademarked and an (R) appeared after the '531', and in 1976/77 the gold band changed to (TI) Reynolds Limited However, sometimes earlier decals are installed in later years.
http://www.ece.ubc.ca/
So I think this bike is either 1974, 1975, or perhaps 1976 with an old decal affixed.
- Don Gillies
San Diego, CA, USA