Code:
nawk -F, 'NR==FNR{a[$1OFS$2OFS$3]++;next} a[$1OFS$2OFS$3]{b[$1OFS$2OFS$3]++}
END{for(i in b){if(b[i]-1){print i";\t\t"b[i]}else{print "NEW:"i";\t\t1"} } }' OFS=, 20111229.csv *.csv | sort
NE:220012,SHELF:5,SLOT:5; 3
NE:220172,SHELF:3,SLOT:4; 3
NE:220251,SHELF:7,SLOT:4; 5
NE:221478,SHELF:10,SLOT:4; 7
NE:221478,SHELF:3,SLOT:2; 3
NE:222372,SHELF:5,SLOT:4; 2
NE:236313,SHELF:16,SLOT:3; 4
NE:238974,SHELF:12,SLOT:4; 2
NE:239160,SHELF:11,SLOT:5; 17
NE:239337,SHELF:8,SLOT:1; 3
NE:267909,SHELF:4,SLOT:4; 5
NE:509033,SHELF:2,SLOT:1; 20
NE:509622,SHELF:12,SLOT:2; 3
NE:554105,SHELF:5,SLOT:5; 7
NE:564127,SHELF:8,SLOT:4; 2
NE:565538,SHELF:10,SLOT:4; 3
NE:565538,SHELF:7,SLOT:4; 17
NE:565769,SHELF:5,SLOT:2; 2
NE:571452,SHELF:11,SLOT:5; 5
NE:571528,SHELF:1,SLOT:5; 2
NE:571528,SHELF:12,SLOT:5; 4
NE:575322,SHELF:8,SLOT:1; 3
NE:602312,SHELF:3,SLOT:2; 3
NE:828273,SHELF:2,SLOT:2; 8
NE:829608,SHELF:1,SLOT:6; 2
NE:851568,SHELF:5,SLOT:6; 5
NE:851608,SHELF:4,SLOT:2; 11
NE:852991,SHELF:11,SLOT:4; 21
NE:858436,SHELF:6,SLOT:5; 3
NE:903793,SHELF:3,SLOT:2; 2
NE:978303,SHELF:3,SLOT:2; 2
NE:993180,SHELF:2,SLOT:6; 4
NEW:NE:220151,SHELF:6,SLOT:1; 1
NEW:NE:221768,SHELF:4,SLOT:6; 1
NEW:NE:223142,SHELF:11,SLOT:5; 1
NEW:NE:236260,SHELF:15,SLOT:5; 1
NEW:NE:504024,SHELF:4,SLOT:2; 1
NEW:NE:573910,SHELF:5,SLOT:4; 1
NEW:NE:597708,SHELF:11,SLOT:5; 1
NEW:NE:883948,SHELF:10,SLOT:2; 1
NEW:NE:972774,SHELF:5,SLOT:2; 1