If you write it accurately it will work as well as any other notation; it doesn't take much use of ABC before you can sightread simple stuff like my little march tune directly off the ABC source. The medium doesn't matter. I did a talk on it once and started by writing "Mrs MacLeod" on a slate.

Obviously the musicians you were with did understand the notation they were using, whatever it was. (20 years ago, it couldn't have been ABC). You were the odd one out.

The first textual music notation I saw described in detail was developed by Ken Loosemore for his masters thesis in Edinburgh around 1976. It was intended as a readable syntax to program a PDP-11 controlling electronic instruments - if the backend wasn't MIDI, it was functionally equivalent. I used to have a copy of the thesis. There may be some of my ideas in it, I remember talking to him about how to represent rhythmic constructs in the most general way feasible. It was a bit more verbose than ABC but also better defined.

There was also some notation developed in the US in the 1960s - for ethnomusicological databases, I think. It was horrible, you had "shift octave up" and "shift octave down" operators so you had to know the complete playback history to tell what any pitch was.

Incidentally, ABC can represent stuff that staff notation can't. Notes given durations like A3/7 will play just fine in ABC players like BarFly, even though no staff notation for that exists.