Use of repeated numerical prefixes for substituents on methane
According to Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013,


  P-14.3.4.2 The locant '1' is omitted in substituted mononuclear parent hydrides.


For the compound $\ce{CHCl3}$ (chloroform), the parent hydride is methane, which is mononuclear. Hence the locant '1' should be omitted in the preferred IUPAC name (PIN); it is simply trichloromethane.