I find that the definition of supplementary angles is given in a couple of different ways.

- Two Angles are Supplementary if they add up to 180 degrees.

or

- Supplementary angles are pairs of angles whose measures add up to 180 degrees.

When the measures of 3 angles add up to 180 degrees, version 2 says they are not supplementary, but version 1 does not exclude that possibility, therefore seems to allow it.

Which is “correct”?