I think the American Standard Watch Case Company was making watche cases for others besides Bulova at this early time. While American Standard was trademarked by Bulova, with noted first use August 1, 1918, I don't remember when Bulova aquired the company?
I'm gonna search my images and books too see if I find American Standard W.C.C. was used by other watch manufactures post 1918. Just because American Standard was first used by Bulova Aug 1918, that doesn't necessarily infringe on American Standard W.C.Co. from using this signature post the date of first use recorded by Bulova. After August 1918, all cases made for Bulova may have said "American Standard", and those made for other watch companies could have been hallmarked "American Standard W. C. Co.". This practice would have most likely stopped completly when Bulova aquired ASWCC, which may have been years after 1918.
So I agree with Lisa's theory, as it relates to cases made for Bulova. However the ASWCC could have been used by other companys for a few more years.