It wasn't a dedicated line, it was inconsistent labeling of a specific model. Just like the xd-m was inconsistently labeled as labeled as XD(M), XDM, XD-M, and XD with a superscript M on it. Springfield also did the same with the XD-E, and the XD Subcompact, which is still often referred to as an XDS or XD(S), just like the single stack.