Jesus anointed

All four gospels comparison, stories with similarities and supposed contradictions

See gotquestions.org text or Bible Munch video
See pastor Mike Winger's video in a series on the Gospel of Mark. It's a long video (72 minutes). Maybe it could be sufficient to watch shorter clips of the video,  incorporated in the worksheet below.
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.
These are the Bible passages:
  • Matthew 26:6–13 with NIV heading Jesus anointed at Bethany
  • Mark 14:3–9 with NIV heading Jesus anointed at Bethany
  • Luke 7:36–50 with NIV heading Jesus anointed by a sinful woman
  • John 12:1–8 with NIV heading Jesus anointed at Bethany