There is no point in getting a retailer to check stock for you unless they leave it on for at least 30 minutes and turn it upside down or right way up depending on your intention. With the current JVC chassis, they do migrate up to a whole pixel during warm-up, and if you flip them over their behaviour is different again. On my X75, blue shifts almost a whole pixel upside down, but doesn't move if its right way up. Fortunately as it shifts near enough a whole pixel, it just takes one click on the convergence adjustment and its sorted. Also blue convergence is the least important. As pointed out above, it is red/green convergence that really matters. On my X75, it is not as good as mentioned above which sounds exceptional, but it remains within 0.5 of a pixel over the whole image, with the worst being at the bottom of the screen. The centre section is within 0.25 of a pixel.
Just a side note, a really good projector with excellent optics will show up even 0.25 of a pixel obviously if your nose is pressed against the screen. The better it is at resolving detail, the more you will see even the slightest misconvergence! Also those JVCs with e-shift devices cause a slight flaring, normally on red, so red pixels appear slightly thicker than they should (even with e-shift off). As a result, you can actually get red to appear above AND below green. It is so easy to obsess about convergence....my X70 was not great. Upside down blue rotated anti-clockwise as it warmed up, while red rotated clockwise. These sorts of errors are near impossible to optimise. With that one I had a choice of okay centrally but dire in one corner (about 1.7 pixels deviation). Or within 1 pixel over the entire screen but out about 0.7 in the centre. This is still within JVC tolerances by the way.
Anyway, it is a bit of a lottery with convergence, but please do not aim for 0.1 or 0.2 pixels over the whole screen because that really is like winning the lottery!