This convention might have been used in 1947 as well, however, we have not found any Raleigh examples from 1947 so far that exhibit this serial system.
In addition to the two serial types above, a third system appears to have been established in 1955, or at the earliest, 1954; terminating in the early-mid '60s - the most recent example I have on hand is from 1962, though I suspect the official cutoff may date to 1963 or '64.
4-5 digits followed by two letters (or, for the 28"-wheel models, two letters followed by 4-5 digits).
e.g.: "12345AB," or "AB12345." Serial "rolls over" when numerals are used up - without rhyme or reason relating to month or year - in the same fashion as an odometer.
"T" serials replaced "P" serials sometime mid-year 1950.
Digits or letters in serial do NOT relate to month/year/day codes; only the serial in whole determines the year.