Dear All STATALIST members

I have a quick question about making treated column after policy effective date

There is effective date of the certain policies for certain counties.
I would like to change the whole date as the policy treated date of certain counties after the effective date.

For example, the policy start date of 1001 county is Nov. 2008. And I want to change whole “policy applied“ column as 1 after Nov. 2008 like below.
But, I only have “currently” column after merging with policy date file.

County Year Month Currently Policy applied
1001 2008 10 0 0
1001 2008 11 1 1
1001 2008 12 0 1
1001 2009 1 0 1
1001 2009 2 0 1
…
…
…
1001 2014 10 0 1
1001 2014 11 0 1
1001 2014 12 0 1
What I did was:

g tm=ym(year,month)
gen lastdate = 659 // Dec. 2014
order tm lastdate Currently
gen difference = lastdate-tm
bys county year month: egen effective=max(Currently) if Currently ==1
replace effective=1 if difference~=0

I know the last coding was incorrect…because that will make all the past months “0”.

Please give some idea of how to change the policy applied column from 0 to 1 after the effective date.
Hope this question makes sense.

Thank you for your help in advance.