Compilation error[ORA-02289: sequence does not exist] ,even if dbVersion '9.3.350',so strange!

Question

I know the reason is that PL/SQL is pre-compilation, so now dbVersion < '9.3.350', even if I don't need get REFDESIG_ID_SEQ.nextval ,
it will also cause this compilation error. So my question is how should I code that?
When dbVersion < '9.3.350' , no sequence REFDESIG_ID_SEQ, just print '1####';
else get REFDESIG_ID_SEQ.nextval , then print '2####'
But now even if dbVersion < '9.3.350', it will cause compilation error[ORA-02289: sequence does not exist] .
How to resolve this? Thanks a lot.
declare
    maxid   number;
    nextid number;
    agileid number;
    v_date  date;
    dbVersion varchar(8):=0;
begin
  select substr(value,1,7) into dbVersion from propertytable where parentid = 5001 and propertyid=37;
        DBMS_OUTPUT.PUT_LINE(dbVersion);
        if (dbVersion < '9.3.350') then
              DBMS_OUTPUT.PUT_LINE('1####');
        else
              DBMS_OUTPUT.PUT_LINE('2####');
              select REFDESIG_ID_SEQ.nextval into agileid from dual;
        end if;
end;

Answer 1

In my DB, If dbVersion < '9.3.350' , no sequence REFDESIG_ID_SEQ
When dbVersion >= '9.3.350' ,sequence REFDESIG_ID_SEQ will exist,
Now my dbVersion < '9.3.350' , and this pl/sql also cause this error.
SO how should I to resolve it ?
Now I need a test case, if dbVersion < '9.3.350' , then print '1####';
else , get REFDESIG_ID_SEQ.nextval   firstly , then print '2####'
How should I code?Thanks  a lot.