[Blog Post] MSI at last!

[asteckley]

... this is why "k" and "l" were added in the smaller more recent handwriting on the right, in a 4th column.

And the partial fourth column seems to continue down from there for two more rows (with what is possibly an "m" and and "n"?).  Then the writer has put two vertical lines through those four rows to isolate the original third column.
(The last of these four rows appears to have an upper-case "N" in the third column rather than the lower case one.)

It all does appear to be a kind of trial-and-error doodling.