Uh oh. Would you even be able to bring these back to the bank? Do these types of markings invalidate the note in any way?
My guess is the X was for a single note to be removed whereas the single line was for the entire sheet. Is it just a coincidence that the last 3 digits are the same on the single note and the sheet notes? That one didn't come from the same block, did it?
Sorry, more questions than answers from me.