Im sure you guys basically know this, but wanted to give my opinion.
I have legs of different length... maybe like 1/2 inch difference so that my left leg is SIGNIFICANTLY larger and more muscled than my right. NO ONE of any medical experience would ever judge leg length in a seated position - its entirely too easy to present inaccurate leg lengths even accidentally. The only way you measure leg length is have the person lie flat. The clinician needs to lift the clients legs with the client completely relaxing the leg muscles, and lower them - then measure from hip bone to the sole of the foot.
Or, they could just eyeball it with jeans and boots on.... that could work.