The project is officially complete!
The display unit displays the hexadecimal digits, as intended.
Problem mentioned in the last log most probably was caused by bad solder joint, or shorting; anyway it was intermittent, and after assembly it "solved" itself - as no wire now moves, all digits are displayed correctly, regardless of input combination.
Now, assembled, it looks like this:
In the video below, the display is half-assembled, and run from low-frequency clock, to show it's workings:
In an assembled unit, refresh rate is 79 Hz. This way there is almost no ghosting, and inactive segments are dark.
All digits supported by the display are shown on photos below:
Final tally of used components:
Some 50 of the components are superfluous, because they belong to parts that were deactivated (because the circuits were wrong). Total number of used parts is 879 pcs.
Views from sides:
On this side board one can set the displayed numbers through the use of switch banks (red), every four switches are coding for one hexadecimal digit in binary. Secondary input mode is through pin headers (yellow).
This side board is ad-hoc additional board made to replace a part of base structure that was in error. Also here is a clock circuit which is much slower than original clock, so that ghosting is minimised.
And final side view is from the power input side, the four main boards are visible edge-on.
The display is done, any further possible changes will be cosmetic in nature (may be I'll add the enclosure in future), so the project can be thought of as complete.