General Data streaming question
Very good question! There are various ways to double check the accuracy. In this case, what I advise is to pick 5-10 random bricks or extreme cases (like corner bricks or top/bottom bricks) and manually measure the distances in the 3D-model and verify the distances in Grasshopper. We did a pavilion ones, while working for Rojkind Arquitectos (http://www.designboom.com/architecture/rojkind-arquitectos-portal-of-awareness/) and we double checked the data also by manually picking some elements and verifying them in Grasshopper (in this case the color division + position of the cups), before fabricating.
Another method is to use a manageable amount of elements first, like say 20. This way it is relatively easy to manually check in the 3D model if the measurements are accurate and conform the data you're measuring in Grasshopper. If everything checks out OK and you set up your def correctly, you can increase the amount of elements to whatever amount you want like 2000 and still be sure the measurements will be accurate for fabrication.