Could this be your John?What is your source for siblings of your John?
1880 census Lee Co, MS:
Category: Name;Relationship to head of household; Marital Status; Gender; Race; Age; Birthplace; Occupation; Father's Birthplace; Mother's Birthplace.
Sallie CALDWELLSelfWFemaleW36MSKeeping HouseTNSC William J. CALDWELLSonSMaleW13MS------ Neffie CALDWELLDauSFemaleW11MS------ Maidee CALDWELLDauSFemaleW8MS------ John CALDWELLSonSMaleW4MS------ 1920 censusfor J. T. lists a son Harry, and 1930 he is Harrington, I do not see a Nick.
Combined info from TX Dth Idx and SSDI (Soc Sec Dth Idx):
Caldwell, Harrington T., b 5 Sep 1912, d 27 Jun 1977 Bexar Co, TX; last residence San Antonio, Bexar Co, TX;SS card issued in TX.