
After he finished, [official scribe Jacob] Shallus had to deal with several mistakes that he had made during that rushed weekend of exacting labor. […] But he also used a penknife to scrape away an entire line of text near the bottom of page one, leaving behind a roughed-up band that now appears gray from grime.
https://www.archives.gov/publications/prologue/2012/fall/const-errors.html
So it would seem to have been a transcription error that was scraped off.













Halley is the one who predicted its return mathematically. I’d say that’s more significant than seeing it twice in one lifetime and supposing that it’s the same comet.