How do you score a walkover, a forfeit, and a no-show?

Keep them separate, because they are different behaviors.

• Walkover. The opponent never answered, or the deadline passed. The result goes to the other player and no match was played.
• Forfeit. The match was accepted and then abandoned before it was played.
• Retirement. The match started and one player stopped. The completed part of the score is recorded with a retirement marker.

None of the three counts as a played match, which matters at the end of a season because playoff qualification is gated on matches played. The definitions.