No, Merioneth never got as far as OFF and certainly not SFF. Along with Motherwell and Wishaw (GM) and Gateshead (FT) they were one of the slowest-issuing councils and only got half way through the original style before the new system came in.
The furthest Merioneth got with the original issues was HFF, which commenced in April 1963, before they switched to the suffix system along with most others in January 1964 when AFF 1B was issued.
Both OFF and SFF are what the DVLA quaintly call 'age-related plates', issued recently to pre-1964 cars which have had their registration numbers either sold or otherwise lost to them, and which of course to most people would appear to be genuine original plates but which to me stick out like a sore thumb! Others codes used for such issues are 'SU' and 'SV' and some others which I just can't recall off the top of my head right now..
