If you are doing tests, just include a sheet of paper or card with the relevant information in the image area (e.g., "f/32-1/15-#25").
If you are bracketing, then it should be rather straightforward to line up the exposures from less to more. The same with differing filtration; it should show up in the image itself.
FWIW, though, I notched my filmholders corresponding to holder number about a century ago and am more than happy I did. I have two sets of notched/numbered holders, one in the U.S. and one in Europe for a total of about 70. The notches are only difficult to see once in a while when they fall in a completely dark area of image (clear on the neg), but subject matter usually makes it easy to tell which is which. I use the numbers as part of my cataloging system. All the keeper negs go into four-sheet pages in roughly chronological order; these go into binders which are then numbered. The negatives are then identified as Subject-Binder#/Neg# (e.g., RockyCove-31/55). Often I'll have two of the same designation in one binder, but the subject matter, again, tells them apart.
Best,
Doremus
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