AC machine could hold a lot of gas in it's pipe work and if no one recovers the machine itself after each use can get a false reading of what came out of car,use to happen a lot where i work till a few guys left.But most likely is that someone was leaning on the machine whilst it was recovering gas and upset the scales on it,again someone used to do that.If that much extra gas was in system AC could have been very noisy and performing very poorly as compressor working too hard or re-leaf would go off with quite a bang.