All the ones I did from Blackpool were on summer Saturdays. And generally class 40s with the Blackpool excursion rake of Mark 1s (I think it was mostly FKs iirc).
Around Nottingham'/Derby/Leicester and in Scotland the adex's were generally on a Saturday - typically not many freights on a Saturday so traincrews and route knowledge tended to be available when required.
In my experience in the 1970s, most Adex and Mystex trains actually ran on Saturdays....with the exception of trips from the Southern Region to the Great Eastern lines (Clacton, Diss for Bressingham Gardens, Norwich, Yarmouth, Cromer and Kings Lynn) which were usually on Sundays.
Can add Oxford and Edinburgh to that list, from Leeds anyway.
Probably not huge money-spinners if all their costs were attributed reasonably sensibly. Perhaps the costs of the really ambitious and lengthy ones were cross-subsidised by the more prosaic and shorter ones to a degree.
Some great pubs in Stockport....plus the hat museum!
Portsmouth Harbour - both via the direct and via Eastleigh - was a popular destination for Mystexes from other regions in the 1970s. Invariably worked by class 47s - which Woking and Eastleigh men signed - they originated mainly from South Wales, the Midlands and East Anglia....which allowed sufficient time in Pompey for a trip over to the Isle of Wight for those passengers who were so inclined.
I think that you're probably right.
I did a few of the Carlisle originating ones in the late 70s including the last two on the list.
Mitre Junction was usually favoured for a traction changeover if heading to the Southern. Certainly was for the Portsmouth and Canterbury/Dover trips I mentioned but unsure for the Southampton/Bournemouth one.
The Carlisle - Southend Central of 3/8/89 is notable for being a class 85 throughout. https://www.sixbellsjunction.co.uk/80s/890803br.htm
Southampton & Bournemouth on the Manchester division ones was normally a Birmingham New Street changeover presume it would be similar for a Carlisle originator?
It was just part of the job in 1976. At Crewe LMR operating HQ there were 4 sets of 4 people for the region re-doing the regular diagrams every week to take account of the engineering work, diversions, diesel-hauling (of electric locos pan-down), footexes, mystexes, charters, strengthened D- or EMUs etc. that were in the STN (4 people for each part of the regions because 1 was doing loco alterations, 1 DMU alterations, 1 doing the "men" and another - I can't remember now, maybe Unit men and loco men were 2 jobs.
I thought it was using stock and locos that would otherwise have been standing idle.
Royal trains were diagrammed on a "need to know" basis by the Service Group heads, the Special notices and books of traincrew workings hand-distributed to named individuals only in HQ and the Control. I don't know what happened "outside."