As the description states, this bitmap flags which fields in this same row have been declared invalid, meaning those specific values should be treated as untrustworthy rather than simply disregarded. If the optics briefly lost lock or the card was mid-reset during this History bin, this is the bitmap that tells you exactly which of the counters and readings in the same row were captured during that unstable window, so they can be excluded from an SLA or trend calculation instead of silently averaged in. For example, a bit flagging the quality-average field as invalid in this row means that particular reading should be dropped from a monthly trend chart even though the row's other counters may still be perfectly valid.