Question about rules

Question about rules:

Let's assume that a language B develops from language A over 2000 years
following a set of transformation rules AtoB. Independently, a second
language C develops from the same language A over 4000 years following a
set of transformation rules AtoC.

A ->-> (AtoB) ->->B
A ->-> -> -> -> -> (AtoC) ->->->->->->C

Due to lack of written and archeological resources we make the honest
mistake to believe that the development followed the sequence

A ->-> (AtoB) ->->B -> -> (BtoC) ->->C

where BtoC is the erroneously perceived rule which in reality is the
difference AtoC-AtoB.

Does any linguistic method exist to help us detect this kind of errors?

Best regards,

Paul Alesu