How can these sometimes be errors receiving credit and sometimes be errors and not receive credit?

ts05_ a048_ ps0000_ 2--  	Error	4/17/10 06:16:23  	4/18/10 17:36:51  	22.25  	559.5 / 0.0
ts05_ b371_ ps0000_ 1-- 	Error 	4/14/10 20:45:13 	4/18/10 02:24:28 	35.40 	603.9 / 0.0
ts05_ b213_ ps0000_ 1-- 	Error 	4/14/10 20:31:24 	4/17/10 11:06:35 	15.87 	330.6 / 0.0
ts05_ a436_ ps0000_ 0-- 	Error 	4/14/10 20:07:19 	4/19/10 02:22:15 	85.32 	864.7 / 864.7
ts05_ a405_ ps0000_ 1-- 	Error 	4/14/10 20:04:42 	4/16/10 12:18:41 	25.86 	782.5 / 782.5
ts05_ a399_ ps0000_ 1-- 	Error 	4/14/10 20:04:13 	4/16/10 15:43:58 	36.37 	372.0 / 0.0
ts05_ a384_ ps0000_ 0-- 	Error 	4/14/10 20:02:35 	4/16/10 15:28:23 	35.40 	603.9 / 0.0
ts05_ a325_ ps0000_ 1-- 	Error 	4/14/10 19:55:28 	4/15/10 20:28:19 	19.24 	484.8 / 0.0
ts05_ a318_ ps0000_ 0-- 	Error 	4/14/10 19:54:35 	4/15/10 10:26:20 	10.70 	311.4 / 311.4
ts05_ a314_ ps0000_ 0-- 	Error 	4/14/10 19:54:02 	4/16/10 11:11:28 	25.73 	767.4 / 0.0
ts05_ a293_ ps0000_ 1-- 	Error 	4/14/10 19:51:38 	4/15/10 04:21:19 	4.57 	115.0 / 115.0
ts05_ a266_ ps0000_ 0-- 	Error 	4/14/10 19:48:24 	4/16/10 11:17:19 	26.81 	799.8 / 0.0

That's over 200 hours of code 29 errors that might or might not be WU errors, with no credit granted.
Maybe I missed something, but what is the exact explanation for this discrepancy?