This subject of note size comes up again and again as the years pass, and nothing is ever resolved. People who believe that older series notes are supposed to have one size and one size only will continue to believe this after the discussion dies down once again.
If you handle enough 1954 and multicolour series notes, you will realize that they were not produced uniformly. You will see notes with big margins on one side, small margins on the opposite side. You will see notes with sloping margins due to the original sheet being rotated slightly out of alignment with the cutting blades. You will see notes with a combination of poor centering and edges that are not orthogonal. All these notes with imperfect features could not have been cut by hand.
Oversize notes happen. They likely come from the edges of sheets rather than the middle.
I seem to recall reading a post a few years ago written by a certain editor of a certain paper money catalogue on the subject of note size, and it mentioned that sheets were not always uniformly dried prior to cutting. Cotton fibre paper tends to swell when wet and shrink when dried such that differences in the size of the printed area of a note can vary considerably. So any discussion of note size needs to take into consideration measurements of printed area in addition to measurements of total size. A note with large white borders may have a smaller printed area than most other notes.
I doubt there will ever be a definitive study done on note sizes because it requires a great degree of expertise, including the ability to recognize altered notes. Trimmed notes would obviously pose a problem to data sets, but also, cleaned/pressed notes will also have their dimensions altered. Notes that have been cleaned and/or pressed tend to be stretched larger than their original size. To do a study, a person needs access to a large and varied stockpile of older series notes in ORIGINAL uncirculated condition. As time moves forward, this becomes more difficult as the number of notes meeting the required criteria dwindles and becomes increasingly disbursed. It also does not help matters that the majority of people, including experts, have trouble identifying notes that have been altered.