As the platen moves the ribbon is rolled up on the spindle. That means each time the key strikes it hits a different part of the ribbon. If the ribbon has been rewound a number of times, or amateur re-inking has been employed, it will almost certainly never print the same letter exactly the same way ~ not even in the same word.
Someone else can verify the movements on any particular manual typewriter BTW,
At what point do we conclude that the change is too extreme to be explained by your theory? (not to mention the kerning.)
Bad ink ~ not kerning. That's a cloth ribbon, not a carbon ribbon.
So, now bad could it get? Well, unreadable. You could get a dirty set of keys, a ribbon reinked by amateurs (rather than just getting a new ribbon they'd ink it), and cheap paper ~ I am sure you could get all sorts of garbage.
Ask your grandmother. She might know.