Thread count in "quilting cotton"
 

What is the thread count (each way) in quilting cotton?

Does it vary from company to company? Does a company vary the count from line to line?

Another factor of the fabric quality/ suitability for quilting has to do with the size of the individual threads within the fabric. For example homespun has thicker threads so a lower thread count yet a thicker fabric. While batiste has very thin threads yet a higher thread count but still a sheer fabric.
Personally I go by feel and appearance when determining whether I want to use a particular fabric in a quilt. And that may differ from one quilt to another.

Yes a company can vary its thread count from line to line. An example is some fabrics have a very highly defined print some with fine metallic... these are typically printed on a higher thread count so the printing will be sharper/clearer . Using a lower thread count fabric for the same print would result in "gaps" these would be perceived by your eye as just not as sharp edge to the design being printed because the printing had no thread to land its color/image.

Not a big concern in quilting fabric but if the thread is wrapped, each wrap is counted in the thread count. This why thread count in sheets are deceiving.