I don’t knot the thread like in the picture. I anchor it into the fabric.
1 - Pass the thread through the fabric once, leaving a short tail. 2 - Pass it through the same spot to form a loop, keeping that tail from step 1. 3 - Pass it through the loop, but not all the way to form a second loop. 4 - Hold the tail, pull the second loop to tighten the first loop down to the fabric. 5 - Pass your thread through the second loop and tighten down to the fabric. (Sometimes I do a third loop before this step, but not always.) You have now anchored your thread.
Yes, you can tell which specific typewriter was used to type something so long as there is either a slight defect (for lack of a better term) if two letters are closer to/further from each other or a letter is a little higher/lower than it normally is.
PLUS, because different people hit the keys with different amounts of force, each machine wears out at different rates and so the keys wear out at different speeds, so there’ll be different wear patterns to the keys.