Reversion v reversal

If you are in the mood of thinking of tests, my feeling the difference in the meanings of ‘reversion\ reversal’ is so subtle that it takes a very sophisticated native speaker to spot it.

“This is a complete reversal of the terms as they were originally laid out in the last will and testament.” … l-test.php

‘Reversion’—“an act or process of returning to an earlier condition or state”
‘Reversal’—“ a change of decision or direction, often to the opposite”; ”the act of changing or making something change to its opposite”

– From the original, you could hardly gather how much the terms of the will were changed: whether they were rewritten ‘to an earlier state’ or changed to the opposite. ‘Complete reversal’ seems to sound equally valid to ‘complete reversion’.
Not the test to take on this very day surely?

Q: What did Adam say the day before Christmas?
A: It’s Christmas, Eve!