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=, 20111228.csv *.csv | sort
NE:221478,SHELF:13,SLOT:4; 2
NE:221726,SHELF:8,SLOT:1; 2
NE:222318,SHELF:14,SLOT:1; 9
NE:222799,SHELF:5,SLOT:2; 2
NE:230478,SHELF:10,SLOT:6; 2
NE:252848,SHELF:3,SLOT:5; 3
NE:267909,SHELF:1,SLOT:6; 2
NE:267909,SHELF:4,SLOT:4; 4
NE:509033,SHELF:2,SLOT:1; 11
NE:509622,SHELF:12,SLOT:2; 2
NE:541469,SHELF:11,SLOT:6; 31
NE:565538,SHELF:7,SLOT:4; 15
NE:571528,SHELF:8,SLOT:2; 12
NE:593848,SHELF:3,SLOT:1; 3
NE:594728,SHELF:3,SLOT:5; 32
NE:597708,SHELF:12,SLOT:6; 2
NE:602306,SHELF:18,SLOT:6; 4
NE:800189,SHELF:8,SLOT:3; 3
NE:801048,SHELF:3,SLOT:1; 2
NE:825890,SHELF:5,SLOT:1; 2
NE:852991,SHELF:11,SLOT:4; 20
NE:877073,SHELF:3,SLOT:3; 6
NE:984177,SHELF:1,SLOT:4; 6
NEW:NE:220072,SHELF:6,SLOT:3; 1
NEW:NE:221514,SHELF:14,SLOT:1; 1
NEW:NE:230293,SHELF:6,SLOT:2; 1
NEW:NE:239160,SHELF:15,SLOT:4; 1
NEW:NE:509860,SHELF:8,SLOT:3; 1
NEW:NE:602306,SHELF:6,SLOT:3; 1
NEW:NE:801048,SHELF:6,SLOT:2; 1
NEW:NE:825890,SHELF:2,SLOT:4; 1
NEW:NE:826030,SHELF:8,SLOT:3; 1
NEW:NE:841068,SHELF:8,SLOT:4; 1
NEW:NE:854479,SHELF:6,SLOT:5; 1
NEW:NE:895435,SHELF:5,SLOT:5; 1
NEW:NE:993180,SHELF:3,SLOT:1; 1
#cat 20111228.csv
NE:221726,SHELF:8,SLOT:1,01:00:02,Wed Dec 28 2011
NE:801048,SHELF:3,SLOT:1,01:30:02,Wed Dec 28 2011
NE:841068,SHELF:8,SLOT:4,02:00:03,Wed Dec 28 2011
NE:593848,SHELF:3,SLOT:1,02:30:09,Wed Dec 28 2011
NE:801048,SHELF:6,SLOT:2,04:00:01,Wed Dec 28 2011
NE:252848,SHELF:3,SLOT:5,04:30:03,Wed Dec 28 2011
NE:852991,SHELF:11,SLOT:4,05:30:01,Wed Dec 28 2011
NE:509033,SHELF:2,SLOT:1,06:30:01,Wed Dec 28 2011
NE:509033,SHELF:2,SLOT:1,09:00:01,Wed Dec 28 2011
NE:222318,SHELF:14,SLOT:1,10:00:01,Wed Dec 28 2011
NE:267909,SHELF:4,SLOT:4,12:30:02,Wed Dec 28 2011
NE:800189,SHELF:8,SLOT:3,13:30:02,Wed Dec 28 2011
NE:509622,SHELF:12,SLOT:2,14:30:01,Wed Dec 28 2011
NE:852991,SHELF:11,SLOT:4,14:30:01,Wed Dec 28 2011
NE:602306,SHELF:6,SLOT:3,15:00:01,Wed Dec 28 2011
NE:597708,SHELF:12,SLOT:6,15:30:01,Wed Dec 28 2011
NE:239160,SHELF:15,SLOT:4,15:30:01,Wed Dec 28 2011
NE:800189,SHELF:8,SLOT:3,16:00:01,Wed Dec 28 2011
NE:825890,SHELF:5,SLOT:1,17:00:02,Wed Dec 28 2011
NE:571528,SHELF:8,SLOT:2,17:30:01,Wed Dec 28 2011
NE:594728,SHELF:3,SLOT:5,17:30:02,Wed Dec 28 2011
NE:565538,SHELF:7,SLOT:4,18:30:03,Wed Dec 28 2011
NE:825890,SHELF:2,SLOT:4,18:30:04,Wed Dec 28 2011
NE:220072,SHELF:6,SLOT:3,19:00:03,Wed Dec 28 2011
NE:826030,SHELF:8,SLOT:3,19:00:03,Wed Dec 28 2011
NE:895435,SHELF:5,SLOT:5,19:00:06,Wed Dec 28 2011
NE:222799,SHELF:5,SLOT:2,19:00:06,Wed Dec 28 2011
NE:267909,SHELF:1,SLOT:6,19:30:01,Wed Dec 28 2011
NE:800189,SHELF:8,SLOT:3,19:30:01,Wed Dec 28 2011
NE:984177,SHELF:1,SLOT:4,20:00:02,Wed Dec 28 2011
NE:230293,SHELF:6,SLOT:2,20:30:02,Wed Dec 28 2011
NE:602306,SHELF:18,SLOT:6,20:30:02,Wed Dec 28 2011
NE:541469,SHELF:11,SLOT:6,20:30:02,Wed Dec 28 2011
NE:854479,SHELF:6,SLOT:5,20:30:02,Wed Dec 28 2011
NE:825890,SHELF:5,SLOT:1,20:30:02,Wed Dec 28 2011
NE:221478,SHELF:13,SLOT:4,21:00:01,Wed Dec 28 2011
NE:252848,SHELF:3,SLOT:5,21:00:01,Wed Dec 28 2011
NE:230478,SHELF:10,SLOT:6,21:00:01,Wed Dec 28 2011
NE:509860,SHELF:8,SLOT:3,21:00:02,Wed Dec 28 2011
NE:565538,SHELF:7,SLOT:4,21:30:02,Wed Dec 28 2011
NE:993180,SHELF:3,SLOT:1,22:00:01,Wed Dec 28 2011
NE:852991,SHELF:11,SLOT:4,22:00:02,Wed Dec 28 2011
NE:221514,SHELF:14,SLOT:1,22:00:02,Wed Dec 28 2011
NE:267909,SHELF:4,SLOT:4,22:30:01,Wed Dec 28 2011
NE:877073,SHELF:3,SLOT:3,23:00:02,Wed Dec 28 2011