The transcription on this from .pdf via Hypothesis is dreadful! In particular for the card sizes. The actual text reads as:

1. Devices for note-taking. In taking notes of reading, use slips of paper the size of the standard library card (3 x5 in.). For more extended notes and for typewritten notes, the standard half-sheet (5 1/2 x 8 1/2 in.) is usually the most satisfactory size. For special purposes still larger sheets are sometimes essential. In any extended investigation the use of different colored slips or different colored inks for certain classes of notes will often prove a convenient and time-saving device. It is especially desirable, thus, to distinguish bibliographical data from subject matter. Each slip should contain only a single note. Put a topical heading at the top of each slip of subject notes and a reference to the volume and page of the authority quoted.

This will be much more interesting given that he'd first written about this topic in 1908 and has accumulated more experience since then.

Look for suggestions about the potential change in practice over the ensuing years.

Is the original version extant in his papers?

of course this also depends on the overall quality of the work and not just the length...

One can't help but notice that Dutcher's essay, laid out like it is in a numbered fashion with one or two paragraphs each may stem from the fact of his using his own note taking method.

Each section seems to have it's own headword followed by pre-written notes in much the same way he indicates one should take notes in part 18.

It could be illustrative to count the number of paragraphs in each numbered section. Skimming, most are just a paragraph or two at most while a few do go as high as 5 or 6 though these are rarer. A preponderance of shorter one or two paragraphs that fill a single 3x5" card would tend to more directly support the claim. Though it is also the case that one could have multiple attached cards on a single idea. In Dutcher's case it's possible that these were paperclipped or stapled together (does he mention using one side of the slip only, which is somewhat common in this area of literature on note making?). It seems reasonably obvious that he's not doing more complex numbering or ordering the way Luhmann did, but he does seem to be actively using it to create and guide his output directly in a way (and even publishing it as such) that supports his method.

Is this then evidence for his own practice? He does actively mention in several places links to section numbers where he also cross references ideas in one card to ideas in another, thereby creating a network of related ideas even within the subject heading of his overall essay title.

Here it would be very valuable to see his note collection directly or be able to compare this 1927 version to an earlier 1908 version which he mentions.