I thought it was strange that codify did not return the same variable name for the date of interest as specified in data. Using your example data, ex_people has a date called event but when I combine it with ex_icd10 using codify the resulting data frame has a date variable named date rather than event. I would prefer to maintain the original variable name. This behavior does not occur in other functions; for example, categorize returns the original date variable name even when arguments are passed to codify.
Zabore: