A characteristic of older typewriters (like the IBM Executive) is that they used an individual arm for each lower character and its corresponding capital letter (for a few printing characters that weren't letters or didn't have capitals they would have symbols in the shift position instead). When a shifted character (a capital letter for example) was required, the typist's press on the "caps" key would physically raise the carriage containing the platen roller on which the paper was wound so the "shifted" character would impact the paper through the ribbon instead of the "unshifted" character.
As the typewriter was used, the shifting mechanism rather quickly would become worn so there was a bit of wobble introduced, resulting in characters not aligning with the baseline. Also, because the Executive used proportional type requiring tight spacing, the arms that struck the ribbon/platen roller were very prone to sticking together if the typist didn't maintain a proper interval between keystrokes. When two keys would approach the printing position together, usually one would be slightly ahead of the other and would print, but would be forced slightly out of position sideways by the force exerted by the other arm. So Executive-written letters can be spotted by looking for misalignment of characters along the baseline, and by characters that are slightly to the left or right of where they should appear.
Finally, yet another form of vertical misalignment can occur when the typist is a little bit off when using the caps key. I.e., the typist lets go of the shift key just an instant before a character prints, and the carriage has already started to drop when the character hits the ribbon/platen roller. Or, going another way, the typist is slightly late in hitting the shift key, and the character prints before the carriage has completed raising the ribbon/platen roller. However you get there, typewriters that have been in use for awhile will have characters that don't align. Modern word processors don't produce anything like that.
He goes on to point out the specific examples of this in one of the documents. I'm hamstrung by my birthdate again, but this sounds legit.
