OPDPlanQuantity__c
    if(AND(NOT(ISBLANK(SSlastMonth_Plan__c)) , NOT(ISBLANK(SSBollow_Date__c)), (MONTH(SSBollow_Date__c) = IF(MONTH(TODAY()) = 1, 12, MONTH(TODAY())-1))),1,0)
0907BK
if(ISBLANK(SSBollow_Date__c),1,
if(AND(NOT(ISBLANK(SSThisMonthPlan__c)) , NOT(ISBLANK(SSBollow_Date__c)), (MONTH(SSBollow_Date__c) = MONTH(TODAY()))),1,0)
)
    false
    if(ISBLANK(SSBollow_Date__c),1,
if(AND(NOT(ISBLANK(SSThisMonthPlan__c)) , NOT(ISBLANK(SSBollow_Date__c)), (MONTH(SSBollow_Date__c) = MONTH(DATEVALUE(CreatedDate-15)))),1,0)
)
    BlankAsZero
    
    18
    false
    0
    false
    Number
    false