Ok, I think I have a mental picture of what has been going on here (from the fitting problems, loose bolts etc.perspective) but please bear with me, this is going to get wordy!
Fundamentals (which might not be immediately intuitive):
1. The bottom hinge pins and guides, and the top guide castings, are not responsible for keeping the door closed under cabin pressure differential. This function is performed by the Stop Pads and Stop Fittings. There are 12 of these, 6 on each side. The top and bottom edges are obviously rigid enough to resist cabin pressure without further local support.
2. As a 'plug' door, the stop pads and fitting interlock - The stop fittings on the door must pass inside the stop pads on the frame when the door moves downwards to the locked position. With them interlocked, there's no way the door can open under pressure differential (again, it is a plug design). The clearance between the pads and fittings must necessarily be close - you don't want the door moving out significantly as the cabin is pressurized.
3. Everything else - the hinge pins and guides and the upper roll pins and castings are only there to keep the 12 stop pads and fittings interlocked before the cabiin is pressurized. After this, they play no role in holding to door closed. Their only other function is to facilitate insertion and removal, which only happens on assembly, and probably, major inspection.
3. Fitting the hinge pin guides is part of the door manufacture. Their bolts will have been torqued up during assembly.
What I think is possibly happening at the factory (I've used 'door' for 'plug door' from now on), resulting from poor moral and time pressure:
1. The door must first be lowered onto the hinge pins at the bottom of the door frame. This isn't necessarily easy, the pins must be set parallel and introduced into the guide fittings on the door. First you have to slip on two uncompressed lifting springs onto the pins, then you have to get the ends of the pins into the guide fittings. The pins don't have alignment tapers, instead they have the threaded portion for travel stop washer and lock nuts, followed by a hard shoulder to the full diameter. The door itself weights 36kg. Damn, I can't get both pins in! First possible alignment issue - the spacing hings pins and guides might not match exactly: Possible bodge solution, loosen off the bolts on one of the hinge guides, there, that's better, both pins go in now.
2. Hinge the door in and try to push it down to the closed position. Firstly it needs to be pushed down against the spring pressure that holds it in the lifted position. Compressing the springs will increase the pressure to higher than the 36kgf needed to support it open - probably requires a boot pressure down on the bottom of the door.
3. Damn, the stop pads and fitting won't pass and interlock! Second possible alignment issue: The clearances are tight and something isn't sufficiently aligned - maybe the hinge pin guides, maybe the hinge mounts themselves to the airframe (I wonder if any of those bolts have been found loose!), maybe the roll pin guide fittings at the top of the door. Possible bodge solution, loosen the bolts on the upper guide fittings or hinge pin guide fittings to make the stop pads interlock.
4. Fitting the locking bolts (lower): The door needs to be pushed down against spring pressure, whilst bending right over and trying to push the bolts through from the rear (skin side) of the pin guide casting, whilst trying to align the holes in the casting with the one in the hinge pin (bugger this!). Hopefully it eventually goes in and the assembler isn't too pissed off to fit the castellated nut and pin. Now the other side, trying to do the same thing, only with the other (non favored) hand. Damn, I can't get the second bolt through! Third possible alignment issue: With the door is sitting in the frame, maybe it is impossible to get the other bolt to go through - the assembler is pushing against two springs and effectively trying to move the whole height of the door from side to side! Possible bodge solutions: 1) loosen the pin guide mounting bolts or 2) leave the bolt out - the other one and the top ones will hold it!
5. Top roll pin guide fitting casting locking bolts. This one I find most difficult to understand. At this stage, the door ought to be held down sufficiently by the hinge pin bolt(s). Maybe not if the pin guide mounting bolts have been loosened. Even if not, some downward foot pressure on the door ought to be enough to pull it down low enough for the roll pin to clear the bolt holes. I can't work this one out - worst case, the door is slightly tilted by the shenanigans at the bottom of the door I suppose. Maybe they were forgotten on that one plane and present on all the others under inspection. I'm sure the airlines would have flagged it damned quickly if the had found any of those missing, but up to now it mainly seems to be loose bolts.
6. Have every intention of tightening the awkward to access loose bolts whilst be pressured to get on with the next job.
All of the above might also have been complicated by the door being stuffed with fibreglass insulation. It's not shown in any of the pictures but the rest of the cabin is, so presumably the door too.
I don't think any of the four lock pins bolts need to be torqued up by the way, they are there to block side force and the castellated nut and split/cotter pin will prevent them from coming out, they would need to be backed off until the drilled cotter pin hole is accessible anyway. Worst case, overtigntening could crack the casting.
P.S. The movement stop washers and lock nuts on the ends of the hinge pins may or may not have been forgotten. Possibly one of them was on the lost door. One was certainly there because the ripped off pin guide (rear) was still with the plane. The front one was either not present of was ripped off, if so, there will be stripped threads on the pin and a hell of a witness mark on the plane door. Worst case, they aren't essential, although they could give some engineer a hell of a shock as the door jumps out on him when he opens it!
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