1d081462_Some_Clarifications___WBXPress__Clarifications
[Points of doubt] 4. What will be the date of fixation of pay when such benefit of 10/20 years of service will be available to an employee? [Clarifications] 
Since the date of annual increment shall always remain unchanged i.e. 1st July of the year and there shall be a gap of at least 6 months between any type of increment and annual increment, fixation of pay is to be regulated as per option of the employee for such non-functional benefit and such fixation of pay is to be made as per principles laid down in para 3(i) of the Memo No. 181-SE(B), dated 08.10.2009.
Pay Fixation of Teacher - Some Clarifications – WBXPress
Clarifications