Indeed Messerschmitt did proof checking of their airplanes. I've only seen one such paper, this is for Erla licence-produced Bf 109Gs. You can see the nominal (guaranteed) performance with a thick line, and also the upper and lower tolerance on performance (+/- 3%) for acceptance.
The dots are measured values for 13 individual planes - some are a bit worse, some are bit above the specs, and there are couple that will be rejected until the plane is brought up to spec.
The story in short is, however, the nominal specs are guaranteed to be reached within limits. An aircraft is just like any product, the producer has liability to meet the agreed contract, no matter when, and where. In Germany, the LW had its own separate quality control organisation, the BAL. They were pretty strict right until the war's end. Reading Hans Fey comments on Me 262 testing, the lower limit for the Me 262 was 830 (nominal/guaranteed spec was 870 kph), they did accept planes down to 825 but that was it; anything lower would be rejected. And that was in 1945, when the Germans would need as many jets as possible.
http://www.lwag.org/forums/showthread.php?t=484
Now the bottomline: As shown in the Baubescreibung Me 109E document, the specs for the 109E were 500 km/h at SL and 570 km/h at altitude with 1.35 ata or full power and the DB 601Aa engine, within +/- 5 % of that for each individual plane. We have exactly that aircraft modelled in the sim, so E-1, E-3 and E-4 should satisfy these specs. If they are modelled different, its wrong, end of story.