Wait a second. There have been plenty of bills that I didn't have a yea or nay opinion on, so I just didn't vote, on purpose. I've missed like two or three by accident, the other four were just abstentions
When I was speaker, I always had a separate category for "Abstain" versus didn't vote. Pericles Does this as well, and I assume if there are abstentions to be counted, dfw will as well.
I strongly recommend an affirmed abstention over being listed in the not voting category. The latter exists solely for the purpose of this, weeding out those who don't do their jobs.