Another source of confusion is the treatment of which days night flights are assigned to.
The daily reports all have "Date that data relates to (from 00:00 hrs to 23:59 local time)" on the top line of the report.
However the info for Saturday 4th February (one of the snow days) actually covers the period 04:30 Saturday 4th February to 04:30 on Sunday 5th February.
Hence the continual stream of departures that took off over Cranford in the early hours of Sunday are attributed to Saturday's report and not to Sunday !!
Odd that they clarify the timing of the data on the first line and then don't actually report the info on that basis.
Yes, for some reason night movements seem to be giving the analysts a lot of problems.
It may also be relevant that the night quota dispensation counts for 4th and 5th February were initially shown as TBC, then values were "added after verification" that were actually higher than the total number of movements (exempt/non-exempt), then they were changed back to TBC with the comment "figures withdrawn pending further analysis".
Given the long-standing statutory requirement to report LHR night quota movements and exemptions to the DfT, you would think that any bugs in the analysis and reporting process would have been ironed out long ago.