Expiration Date Based on Shelf_Life

Question

I don't know what is wrong with my code. My code works if the shelf_life is over 1 year. But if the shelf_life is 6 months. It expired very short. It takes only 3 months and it is already expired. But the shelf_life is 6 months. What am I going to do ? What is lacking in my code ?

Week Code: 2138 (2021 week 38)
Shelf_life : 6 months

    CTime tt, t11;
    CString Cweek, Cyear;
    int yy, mm, wknum, yrnum;

    tt = CTime::GetCurrentTime();
    yy = tt.GetYear();
    mm = tt.GetMonth();

    wknum = atoi(tt.Format("%U"));
    yrnum = atoi(tt.Format("%y"));
    t11 = CTime(yy, 1, 1, 0, 0, 0);
    if (t11.GetDayOfWeek() != 1)
        wknum = wknum + 1;

    Cweek.Format("%01d", wknum);
    Cyear.Format("%02d", yrnum);

    
    CTimeSpan shelf_no = CTimeSpan(atoi(view->m_pODBCPartsNo->m_shelf_life), 0, 0, 0);
    CTime expiration_date = t11 + shelf_no;

Week code is a date code, for example 2138, year 2021(21) week 38(38). Week 38 is around September 19, 2021 to September 25, 2021.