IN  의 결과는 테이블의 값을 토대로 20개 단위로 쪼개 놓은 것인 듯 하고
OUT 의 결과는 테이블의 값 그대로 인 듯 하네요? 맞나요?
OUT 은 별도 가공 없이 그냥 뽑으면 되겠네요?

WITH t AS
(
SELECT 1 test_case, 'P1' pallet, 'L1' lot, 15 stock FROM dual
UNION ALL SELECT 1, 'P2', 'L2', 15 FROM dual
UNION ALL SELECT 1, 'P3', 'L3', 15 FROM dual
UNION ALL SELECT 2, 'P1', 'L1', 30 FROM dual
UNION ALL SELECT 3, 'P1', 'L1', 10 FROM dual
UNION ALL SELECT 3, 'P2', 'L1',  5 FROM dual
)
SELECT test_case
     , 'IN' gb
     , DECODE(lv, 1, 'P'||min_pallet, '#'||(lv - 1)) pallet
     , lot
     , SUM(LEAST( cnt
                , stock
                , lv * cnt - (s_stock - stock)
                , s_stock - (lv -1) * cnt
                ) ) stock
  FROM (SELECT test_case
             , pallet, lot, stock
             , MIN(TO_NUMBER(SUBSTR(pallet, 2))) OVER(PARTITION BY test_case) min_pallet
             , SUM(stock) OVER(PARTITION BY test_case ORDER BY pallet) s_stock
          FROM t
--         WHERE test_case = 1
        )
     , (SELECT 20 cnt, LEVEL lv FROM dual CONNECT BY LEVEL < 99)
 WHERE s_stock - stock < lv * cnt
   AND s_stock > (lv - 1) * cnt
 GROUP BY test_case, lv, min_pallet, lot
 ORDER BY test_case, lv, lot
;