The guess is indeed a guess and can be wrong. There are some codes which could be either ICD-9 or ICD-10. The current implementation doesn't check whether the codes exist in any definitions (ICD-9 CM or WHO, for example), just whether they are valid.
guess_version(x, short_code, ...)input data
single logical value which determines whether the ICD-9
code provided is in short (TRUE) or decimal (FALSE) form.
Where reasonable, this is guessed from the input data.
number of elements or rows to sample
Currently, ambiguous codes are guessed as being ICD-9 or ICD-10, with no indication of uncertainty. Possible solutions are adding an attribute, warning, or optionally throwing an error.