Thread by @portalrealm

Further research into the Mirror Darkly Bridge (thread 1/14)

(2/14)
The Mirror Darkly set had been identified as being derived from the Hyde Park exhibition bridge.
Hans Zimmerman had overseen both and the blueprints for Hyde Park had later been stamped with the Enterprise Production label

(3/14)
But there is a problem with the profile between the two bridges - they don't match.
As well as the profile being deeper on the Mirror bridge, the upper displays are forward of the lower black portion. With Hyde bridge, these are recessed.
Mirror also has rounding present

(4/14)
We can see this recess rather more closely on the Hyde part blueprints (with the green arrow)

(5/14)
So if the consoles are not Hyde-type, what sources were used for their design?
Scenario 1: Redesigned completely from scratch (possible, but time and resource consuming)
Scenario 2: Repurposed from the DS9 Trials and Tribble-ations bridge blueprints

(6/14)
Looking at the Tribble bridge blueprint, we have the upper display level forward of the lower black display. We also have the rounded corners.

(7/14)
It should be noted that the original TOS bridge also has these features - Tribbles bridge is more accurate than Hyde.
Image from miri_plt of twitter

(8/14)
The Tribble set was only a partial build, but the original TOS set was segmented - you could just repeat the same segment every 18 degrees.

There is one issue - missing from the Tribble bridge is a viewscreen.

(9/14)
So where do the Hyde park blueprints figure into this? They were stamped as part of the production.

I think the Hyde design was used for the viewscreen, the controls of the various stations, and possibly the central platform.

(10/14)
This sheet was included in the Mirror blueprint bundle at auction, but although the exhibition company name was blacked out, there is no Enterprise production stamp. Perhaps this was an unused sheet.

(11/14)
If the Tribble bridge sheet does indeed form the bulk of the Mirror Bridge, then is also likely the turbolift set is also Tribble based. Maybe the corridors as well.

(12/14)
There were 29 blueprints for the entire Tribble set, and at least 3 of them were for the bridge section.
Although I have managed to produce one clean annotated sheet using several photos, we have no other photos for the other two sheets.

(13/14)
TNG Relics captain's chair and helm were originally made for an exhibition by Steve Horch based on the famous commercially available bridge blueprints.
They would be rented again for Tribbles.

(14/14)
I don't know where the Mirror Darkly helm and chair originated from, but its possible these were the same ones from Steve Horch.
His company did provide a helm targeting scanner for the episode

(15/14)
The captain's chair could not swivel in Mirror Darkly
I don't think Relics or Tribbles could either.