What happens if an athlete's yard crossing isn't recorded?

Their result is unaffected. In a backyard ultra an athlete is only out when they miss the bell or the cut-off, so RunnerBeam presumes every athlete still racing has completed each yard before the one in play, whether or not a crossing was recorded for it.

Yards without a recorded crossing, for example after a signal black spot on the course, are marked as assumed and timed by the bell schedule, so yard counts and cumulative time on feet stay complete. Recorded crossings are only used for per-yard stats such as the fastest yard, and timekeepers can add a missed time by hand at any point.