Leaving from FRA, I was able to visit the LH C Lounge (A Gates) with with J ticket. However, when I asked for lounge access during bag check, staff told me there was no lounge access for me as my flight was leaving from the B gates. Nonetheless, I went through security for the A gates intending to use the above mentioned LH lounge. Lady at the desk was initially confused but let me in when I insisted that my DE J ticket grants access.