My manager wants me count each center that has an order. If a center make one order within the beginning of the last two months, it is considered active for the next two months from the month that it made an order. Example: if center ‘AR238’ made an order in February then it is considered active for the next two months. So it is active until April if it does not make another order in march or April. I am trying to count each active center for each month, compounding from the previous months. So if a center made an order in February I need to be able to count that for Feb, Mar, and April. Please assist on how to do that.