As I know,
users of wikipedia can change their status by becoming helper,
admin or joining other groups. Since when, the user groups like this data
showed, the date this date collected? How I am supposed to do if I want the
data showing the change of user status?
You'd need to check the data from the logging table to see when
user rights were changed on individual users.
-Chad
Also note that some information will be inside meta logs table, and
really old sysopping actions won't be recorded at all.