What puzzled me about the Euston one was that sometimes (but not always) the destination station would also be the last of the calling points (not logical, of course).
It was the way some of the flaps were laid out with the stations on it. Some had the penultimate calling point on the upper panel flap, and the destination on the lower panel flap. Depended on who had made up the cards from the Solari manual. The booked service trains had all the cards made up in the DMO at the start of each new timetable. It was left to us 'on the ground' to make up any 'extras', avoiding duplication of information if at all possible by referring to the manual. Extras were normally made up on the night shift. Problems also arose when the flaps were altered each year. I remember that they were installing new flaps for the Fort William service, the bottom flap read 'Stations on request' (Upper panel) 'The Royal Highlander' (bottom panel). This replaced 'The Ulster' (top panel) 'Express' (Lower panel). However for some reason only part of it was changed, ending up as 'Stations on request - Express'. The only information the operator had was a repeater in the Box showing the Departure/Arrival Time plus the Destination/Originating Main flap. There were no monitors while I was there, and the only time you were aware of problems with the display was if someone actually noticed it and bothered to phone you.
I also remember that when there was a 'lull' in departures (often the aftermath of an IRA bomb alert) in the late 70s/80, with the usual absence of any useful loudspeaker information, the sign that a train about to run was the Solari bursting into action, with the calling points revolving. Waiting for your destination station to appear, and hoping that it stopped then ... but it quite often went through the whole lot a few times. Sometimes then went back to blank, hopes dashed.
I can only speak for the time I was there, but I don't think there was ever a time during the occasional bomb scare/hoax that the trains were ever cancelled off the Boards. I always put the next 10 scheduled services up at all times (even on nights), and they were only cancelled off when the train was actually leaving (you could visually see the trains coming and going from all the platforms where you sat). The situation you describe of the Boards 'Running through' was an indication of a fault with that particular Board. The Set-up consul had a green light on it, this would 'pulse' as the Board was cancelling off or setting up. You could see something was wrong as the green light would remain steadily illuminated for 5 seconds or so, and then pulse again until the Board had cleared. Not having a visual check on the Concourse Displays it wasn't possible to pinpoint the faulty flap immediately. Normal practice would be to try the Board with the same card several times to see if the fault cleared. After the third attempt you would leave that Board blank until you had time to do a proper test. That would consist of putting a Test Card in each flap in turn. If the flap was working okay the green pulsing light would stop and extinguish when the flap was set okay, if it wasn't you would get the steady green light and then the flap would continue to run through until cancelled (If you listened carefully this fault would be accompanied by a 'click' from the consul). It was then possible to use that Board as long as your next display didn't use that particular flap. (You would take the Computer Card and count down the rows of punch holes to see if that flap was to be used). At busy times when you needed to have all the Boards in service it was possible to re-arrange the flap layout on the card to avoid the faulty flap and keep all Boards in service. There was a small machine like an old Credit Card 'swipe' device, you put a blank card in and punched out the slots to form a new display.
One of the main bugbears of the system was damp, warm air on the Concourse would mix with cold air in the gallery behind the boards and sometimes condensation caused the system to break down into a cascade failure. In cases like this the good old Emergency Roller Type display would be wheeled out onto the concourse.
The only times you would find the Boards mostly blank was serious disruptions, and you had three boards set up with various calling points, but headed with the dreaded header flaps of 'Please travel from Paddington', 'Please travel from St. Pancras', and 'Please travel from Kings Cross'.
And the digital clocks at Euston which also used flaps - but obviously with digits on - that had vertical instead of horizontal folds. . They went 23-59 then 24.00 (isn't that 0000? so why did they even have 24 on?) then up to about 24.05 before the hour went over to 00 - happy nights waiting for the 0015 all stations Crewe via Northampton and watching the clock.
Really don't know about the digital clock on the concourse, although the one in the Box did have the strange layout that it went from 23:59 to 24:00 and then almost immediately went over to 00:00.
Must've been after my time there as the night service I remember putting up went 23:30 Glasgow, 23:35 Bletchley, 23:45 Barrow, 00:10 Wolverhampton, 0050 Liverpool & Manchester, 03:50 Watford, 06:05 Northampton.