sh_ and ch_ compose the same words

[Torsten]

For example if we see ok-chor- everywhere and find only 3 instances ot-chor, we can simply assume those 3 times were a slip of the pen.
(ok-chor and ot-chor have almost an equal count, something like 18 and 20, which is very usual for these ch-sh words)

This is exactly the point. We would expect to find <chedy> everywhere and to see only some rare instances of <shedy>. But this is not the outcome we get. <shedy> is not used instead of <chedy> it is used together with <chedy>. We would expect a negative correlation between 'ch' and 'sh', but what we find is a positive correlation.