Paul Yes, No, Maybe!!
The 1953 Plunger models introduced the boxed in type of number plate mounting, which has a big hole for the reflector (up to 1955/56). This plate is flat, the top of the boxed pressing slopes down slightly and follows smoothly into the line of the rear light lens. The early S/A plate appears to be the same, then all change to a smaller hole to mount the reflector, but the light unit and box pressing remain the same. Part number changes because the number plate pressing changes to the small hole type. The last of the plungers would no doubt be fitted with the then current S/A mounting to rationalise parts use as supplies were run out for a soon to be discontinued model.
The later 564 lamp unit is more chunky, and to maintain the smooth aesthetic flow of the line, the later number plate now has an indent to angle the lamp and lens slightly downwards at the rear. Fitting this lamp to the early flat faced pressing results in the lamp cocking up, and can be seen on many restored machines in the absence of the correct 525 type lens, which has a distinct tapered shape.
Your bike could have a flat face part from the '53 change over, or a later indent type pressing, depending on how original and when the parts were made. The line of the boxed in section slopes slightly down in all cases, the lamp unit to suit will match this line.
GB's Emily has the later 564 chunky lens, and you can see the distinct change in the line from box pressing to lens. The earlier lens smooths this transition when fitted to the non indented flat face plate. Correct mudguard has centre rib and hinged rear section with a stylish flare to the lower edge. Also two small cutouts to the blade adjacent to the mounting points on the frame backstays by the saddle spring mount.
Swarfy.
Additional. With my speccys on it's hard to tell but the bike pictured below looks correct.
