The endorsement count is equal to the number of feedback posts which include
an endorsement for a #progress-log
minus the number of feedback posts which do not include endorsements
If one badge awarder has posted an endorsement and a second awarder has posted non-endorsing feedback, the endorsement count is 0 and the badge will not be awarded. If a third awarder adds an endorsement, the new endorsement count will be 1 resulting in the badge being awarded.
For more info on feedback & endorsement...
Refer to #Request-Feedback