I'd pretty much given up the idea of completing the pre-1964 symbols as even though the red prohibition circles had been on a number of signs still around they'd all gone for some reason, two left in the west country on cycling prohibited signs and a couple in Scotland and that was it. The hollow red circles were as rare but luckily two were in London so ticked off the list even though they were removed so quickly at the time I don't even remember seeing them on the road either. The triangles were everywhere but so few left now there are only a handful in the south of England I managed to get to.
I was out for a little walk in the sun today and took the road round the park after half way round for a change, and on the way back something caught my eye at the side of the road, too faded to read and the red circle above looking like a no cycling sign would had the paint worn off, but as I got closer I couldn't see any remnants of text, and realised I'd finally found a red circle only a mile or so from where I live. Then I read the sign below, not only a proper road sign but one I didn't have as it had the final line added about pushing bicycles. There's another the other end of the path minus the circle but my collection now has the most valuable part completed.