I've never seen that serial pattern. Granted, I was also out of the hobby for five years, so someone may have already unearthed it before.
At any rate, that's no matter. Everything here is TI-era Raleigh. Slapping Sir Walter on everything was a TI trademark; the earlier bikes didn't have that either. The simplified cable clip is also indicative of TI-era production (the clips on earlier bikes are a bit more ornate and slotted like the fulcrum clamp), as is the short nosed/short tail front fender (I should have noted that straight away). Lugs are third-gen.
Here's a '52 with the longer front fender:
And here are examples of the Mk.1, Mk.2, and Mk.III lugs:
Mk1 - ?-1955
MkII - 1956-1964
MkIII - less pronounced nozzle cut. 1965-1980
Those thicker stamped brake calipers popped up in 1968, and given that it has clips instead of cable stops, it's safely pre-1973. I'd safely put this bike between 1968-1972.
While the decals and black paint suggest an older bike, it so happens that Raleigh used this decal kit on the gold S22's all the way into 1972 (and a bit into 1973 - probably frame overstock), so seeing it this late in the game isn't out of the question. It's a bike made for a market that would be favorable to a model duplicating what Raleigh offered 20 years prior.
-Kurt