So we can be nearly certain that there is a miswire then. The red wire that leaves the 6 lug strip and goes to the octal socket may not be connected to the correct terminal at the 6 lug strip, though I would check all of the wiring at the 6 lug strips.
The 1 at the black center pin of the RCA jack would make me wonder if the reading is just over 100K, and thus over the range of your meter, but you were able to resolve a 270K reading elsewhere. What I would then wonder is if you have the jumper between the lugs on the volume pot where the black wires connect?
Posting some build photos is still a very good idea.
I found and corrected the miswire, it was the red wire going from B5 to terminal B12, it should have been terminal B13. All the wires should be wired correctly now.
Now the readings on terminal 1, 2, 4 and 5 are all the same. They are 30k ohms and still climbing, exactly the same as terminal 13, I suppose that is correct? If those readings are correct then all the readings are correct now except for the black center pin where there is still no reading at all.
The 1 at the black center pin is not because the reading is over 100k I think, because the reading is capable to read up to 2000k.
Where the 2 black wires connect at the bottom of the volume pot there is a wire going up so that is okay I think.
I have included a photo of the point where the white wire from the black RCA jack is soldered to the volume pot, and there is way too much solder there in comparison with the others, the little hole (not the hole that the wire goes through) connected directly on the volume pot itself is completely filled up with solder in comparison with the other connections, maybe this is the cause that there is no reading at the black center pin? The solder is not so much that it is soldered directly to other important parts or connections though.
I have also checked readings of all the 6 connections directly at the volume pot, and the only one that doesn't give a reading is the white wire connected to the black center pin.
Tomorrow I can make more photo's of the whole if those are still necessary now. Now there is too little light for good visibility.