From the study of the surveying errors contained in Smyth's original survey of the pyramid the fact that the upper northern shaft is a deceptive piece of architecture was established. If you zoom into the antechamber and main chamber area of the building you can see the two sections of the shaft shown on the interactive drawing. The section of shaft that starts inside the main chamber of the building is of an unknown length and needs a robot insrting into it and fully exploring.
The second section of this shaft is the false section which runs from the tunnel at the back of the main chamber, which appears at first sight to also be unexplored and of an unknown length. However, after the analysis of the architecture that was carried out in the Great Pyramid papers and published in July of 2021 it is possible to fully resolve this section of shaft.
The illustration below shows the manner in which the floor of the main chamber was designed, with the 'missing' floor stones shown exactly as they were first discovered by early explorers.
The three stones at the west of the room do not exist, and the manner in which the roof and floor decode indicates that rather than replacing the floor stones that appear to be missing, what should be done is that the other two stones that butt up against the north wall should be removed. When this is done, the termination of the lower of the two upper northern shafts will be revealed as shown in the diagram below.
The chamber is designed with a raised floor so that the second dummy shaft is hidden from view and only revealed when the floor stones are correctly removed. The reason that it is possible to deduce this from the architecture is that Rudolf Gantenbrink's surveying of the upper northern shaft is sufficiently accurate that the horizontal continuation of his shaft measurements perfectly coincides with the floor thickness in the main chamber. There is significantly less than 1cm of vertical error in the surveying measurements.
What is required at this moment in time is for the remaining floor stones to be lifted to reveal the hidden dummy shaft start on the concealed part of the wall in the main chamber - a relatively easy task to perform.