I am struggling in SQL to create a flag based on an interval.

This is my use case:

Table: result

The objective is based on the client_id, I need to flag his activity.

If merchandising_month is between start_month and end_month for a record and merchandising_month is between start_month_12m_before and end_month_12m_before, we flag it to yes, otherwise to no

I have tried to do a CASE WHEN filter but I find null values, I tried also an inner join, but without any success.

There is what I have tried:

select * ,
(
    CASE
    WHEN
    (
        (r1.merchandising_month >= r1.start_month_12m_before)
        AND (r1.merchandising_month <= r1.end_month_12m_before) 
    )
    THEN 'No'
    WHEN 
    (
        (r1.merchandising_month BETWEEN r1.start_month_12m_before AND r1.end_month_12m_before)
        AND (r2.merchandising_month BETWEEN r1.start_month AND r1.end_month)
    )
    THEN 'Yes'
    END
) AS activity_N
FROM result r1 INNER JOIN result r2 ON r1.client_id = r2.client_id

And it gives me the null values for each line not answering to Yes condition

Any help would be very appreciated