Yes I am late to the party, but as I am not invited to GRIDCOIN Slack, I am not able to read the discussion over there, but in my opinion the rules are flowed!
“A project will be automatically Greylisted if ANY ONE of the following requirements are met:
• Projects Work Availability Score (WAS) is Red
• Number of Zero Credit Days (ZCD) > 7 in 20”

Most of the projects have a double check mechanism implemented to check each work unit, with fairly long waiting periods to return a work unit and if the results double check is negative or the work unit is not returned in time or is broken, the work unit is resent to a third computer until the results is conclusive.
So if a project is greylisted or blacklisted for not have WU available, but within the waiting period of the wingman’s result is greater 7 dias, GRIDCOIN will not pay the corresponding GRC for completed work.