Используйте приведенную ниже формулу в столбце C:
=IF((OR(TEXT(B2,"MMM")="Jan",TEXT(B2,"MMM")="Feb",TEXT(B2,"MMM")="Mar",TEXT(B2,"MMM")="Apr"))=TRUE,"JFMA",IF((OR(TEXT(B2,"MMM")="May",TEXT(B2,"MMM")="Jun",TEXT(B2,"MMM")="Jul",TEXT(B2,"MMM")="Aug"))=TRUE,"MJJA",IF((OR(TEXT(B2,"MMM")="Sep",TEXT(B2,"MMM")="Oct",TEXT(B2,"MMM")="Nov",TEXT(B2,"MMM")="Dec"))=TRUE,"SOND")))