Count of Months based on the least transaction month between the current month

MONTHS_BETWEEN({today}, MIN(CASE WHEN {transaction.trandate} BETWEEN ADD_MONTHS({today}, -12) AND {today} THEN {transaction.trandate} END))

Avg Qty Sold Per Month

SUM(ABS(   CASE     WHEN {transaction.type} IN ('Item Fulfillment', 'Assembly Build')     AND {transaction.trandate} BETWEEN ADD_MONTHS({today}, -12) AND {today}     THEN {transaction.quantity}     ELSE 0   END )) 
/ NULLIF(MONTHS_BETWEEN({today}, MIN(CASE WHEN {transaction.trandate} BETWEEN ADD_MONTHS({today}, -12) AND {today} THEN {transaction.trandate} END)), 0)