Is it necessary to mention the years pertaining to Sociologist’ theories in order to obtain full marks? If not, will we be credited for mentioning these years or is it redundant?

This is not necessary.  Candidates are not expected to know the year a sociologist’s work dates too, however if they are making an argument about its merit based on the age of the study – e.g. that it is outdated then the period of writing may be useful.