Ever wonder why single-note replacements are usually in small ranges of about 1,000 notes, or a few multiples of that?
How about why sheet replacements are in bigger ranges from 45,000 to a few hundred thousand?
That's because single note replacements were often just a brick (1,000 notes) of otherwise good notes. Maybe they grabbed a few bricks of notes for this purpose.
Sheet replacements were generally printed in batches of one or more reams of 1,000 sheets. With 45 notes to a sheet, the minimum batch of sheet replacements would be 45,000 notes. If multiple reams were produced, you would get a bigger range. Ten reams would get you 450,000 notes.
You learn something new every day.