1957 Kiev 4 = rarer ?

[dee]

Does anyone know how unusual , among prolific Kiev 4 manufacture , a 1957 Kiev 4 with non ridged meter top cover may be ?
1957 is a magic number for me and is also 10 years from the 1947 Kiev with unique hand engraved script .
I am thinking fitting a replica 1947 script face plate , but am concerned if this may be a less common variant .

Thanks
dee