One of the problems with a laid foundation is the edges tend to be uneven because a tiny gap forms when the thread turns around. To minimze this effect the foundation is worked in two passes. The end result is a more even and more dense foundation. This approach is common in good silk embroidery also. You can't tell whether or not this was done from the surface, you must see the back and you must know what you are looking for.
Laid foundations have to be anchored.
Still no matter how carefully you stitch, if the work is not properly mounted, it is not possible to get top quality work. I have not been lucky enough to see the tapestry.