When you see the huge rolls the fabric is printed on. I think it's a wonder any fabric ends up printed on grain. It must be so easy for them to shift.
So many fabrics are printed off-grain, I no longer fold by selvage. Rather, I eye the grain line and make it straight to my eye on the bottom section (which is wrong side up, making the grain even more visible), then line the top piece the same way. Once I've trimmed the edges and removed the selvage, I can check if it's correct by re-folding after it is trimmed. I often have to do a slight second trim. The only time I've found off-grain to be a real a problem is with plaids and checks. Sometimes they're so far off, they're not salvageable (at least, I can't figure out a way to do it).