Jesus anointed - study

See gotquestions.org text or Bible Munch video
All four Gospels report about a similar incident. It seems that the details show differences. Is it one and the same story written about by four different authors? Or are it two incidents, or even more than two? Let's study this, using the NIV translation.
  • Matthew 26:6–13 with heading Jesus Anointed at Bethany
  • Mark 14:3–9 with heading Jesus Anointed at Bethany
  • Luke 7:36–50 with heading Jesus Anointed by a Sinful Woman
  • John 12:1–8 with heading Jesus Anointed at Bethany