file1:
acct|description|nums
foo-001|foo one|1,12,27,37
foo-002|foo two|1,15,25,37
foo-003|foo three|1,18,25,37
foo-004|foo four|12,18,25,37
foo-005|foo five|12,15,25,27,37
foo-006|foo six|1,12,25,27,37,99

file2:
acct|description|nums
foo-001|foo one|1,12,15,27,37
foo-002|foo two|1,15,25,37
foo-003|foo three|1,18,25
foo-004|foo four|12,18,25,37
foo-005|foo five|12,15,25,27,37
foo-006|foo six|1,12,15,25,27,37,99

file3:
acct|description|nums
foo-001|foo one|1,12,15,18,27,37
foo-002|foo two|1,15,25,37
foo-003|foo three|1,18,25
foo-004|foo four|12,18,25,37
foo-005|foo five|12,15,25,27,37
foo-006|foo six|1,12,15,25,27,37,99