Understanding Society User Support

I previous used understanding society data when it was up to Wave 5 i.e. wave 1-5, in the hhresp data they had a variable called month defining month and year( jan yr1---dec yr1, jan yr2...dec yr2), i.e a_month for wave 1, b_month for wave 2.

Now I have downloaded all waves (up to the present wave) and I can't find the variable "month" in all waves. What is the new variable name if the variable still exists, if not what/which variables will give the same information.