Originally Posted by enasniearth
The aprox 2450 nikon sp starting at 623xxxx were two batches .
First batch of 1456 was completed in may 1962 ,
This camera is probably in this batch of numbers
Second batch of 994 completed intermittently from oct 1963 - jun 1965
As demand for professionals .
Source -- Nikon rangefinder system by Robert rotoloni
Thanks for that. The information I read in Japanese corresponds to the first and larger of Rotoloni's two 1960s "reissue" batches as completed in May 1962, and which is the batch that the OP's SP would be from.