What Dan and I have been saying is that while BS381C-537 is a precise colour, there were variations to the Chipmunks' Signal Red (welcome to the real world).
While the R/W/LG scheme was promulgated for Training Command in 1968, it didn’t appear on the Chipmunk until 1970 (this was H.293, dated 24.6.1970). The DayGlo strips certainly appeared before “around 1963/64”; there are examples dated in very late 1961 – perhaps these were early trails applications?