There are books written on the subject. Without seeing the holes for the stitching of the sack, I personally can't identify sack cotton. It is especially hard to tell for sure when looking at completed quilts. However, those who have studied the samples and seen many pictures can recognize the patterns of the prints.
It was interesting to me to find out that it was during Roosevelt's administration that the sizes of the sacks were standardized. Before the 1930's most of the sacks were plain with the company logo printed on them. Then many companies went with a paper label that could be removed and also came up with the pretty prints.
The Cotton Council printed booklets with ideas for using sacks in clothing and household linens. Commercial patterns also were sold.
I think it is a fun subject!