with tbl as (
select 'ЦП-21838611-1-1' bill  from dual union
select 'ЦП-16945846/1-1' bill  from dual union
select 'ЦП-2094102' bill  from dual union
select 'НП-0000053/3/1/1' bill  from dual union
select 'ЦП-6278-0000030' bill  from dual --!!! new bill
)
select bill_full, -- Исходный номер
       bill, 
       bill_shrinked,
       COALESCE(SUBSTR(bill_shrinked,1,INSTR(bill_shrinked,'-')-1), bill_shrinked, 
                SUBSTR(bill,1,INSTR(bill,'-')-1), bill) AS rezultat -- результат!!!
FROM
(select bill bill_full,
       SUBSTR(bill, 4) AS bill,
       SUBSTR(bill, 4, INSTR(bill, '/') - 4) AS bill_shrinked
from tbl)

       COALESCE(SUBSTR(bill_shrinked,1,INSTR(bill_shrinked,'-')-1), bill_shrinked, 
                CASE
                     WHEN  INSTR(bill,'-',-1) > 0 AND
                           LENGTH(SUBSTR(bill,INSTR(bill,'-',-1)+1)) > 6 AND 
                           INSTR(SUBSTR(bill,INSTR(bill,'-',-1)+1),'-') = 0 AND
                           INSTR(SUBSTR(bill,INSTR(bill,'-',-1)+1),'/') = 0 THEN 
                 LTRIM(SUBSTR(bill,INSTR(bill,'-',-1)+1),'0')
                 ELSE NULL END,                                                                    
                SUBSTR(bill,1,INSTR(bill,'-')-1), bill) AS bill