You are OK in your use of terms.

• Precision = ability to recreate consistent results (even if the results are incorrect). If you have a consistent power balance, a single sided PM could be precise, but still inaccurate.
• Trueness = ability to report close to the actual value. If you have a variable power balance, a single-sided PM could be true but inacurcate.
• Accuracy = combination of Precision and Trueness. Unless you have both a 50-50 power balance that never changes during the course of a workout, only a dual-sided PM can be accurate (both True and Precise).

A single sided PM may be Accurate (or perceived to be accurate) for some. But they are not for the general population.