There is zero way the DSC runs are manual - only corrects and adjustments to fix omissions.
Why?
Consider the numbers of bookings over time. Even over a 5 day period (or however long the promo booking periods are) you're talking thousands, probably tens of thousand of bookings that would have to be processed, and even then they are obviously being flown all through the promotion period.
Almost certainly the "incosistent" application of DSC is due to poor coding in the bath runs and/or incomplete data being fed in.
Obviously I've never worked on these systems, but I imagine they run a regular batch run daily, or peraps every couple of days.. I'd imagine it goes through, processes the new enitries for flights registered (ie: new flights posted to account activity) since the last run, then probably have to reconcile those PNR's against registrations and eligibility requirements for the promotion(s) and then process. So you can have a mix of the data not coming through correctly, not being processed correctly due to coding errors or likely input data issues (unexpected entries, or malformed data for whatever reason) and so on.. result.. most of the time things work great but probs may (and do) occur
again this is just a guess, but I'd be shocked if it was far off how the sweeps run.
Certainly no way there's manual mass processing of promotions. IMHO