SKD12 is Japanese version of A2 steel. Even though minor variations might exist they are unlikely to be material. What has always been confusing to me is when steel is reported as SKD because without a number next to it it can be any number of steels that are very different to each other. It is generally accepted that SKD is SKD12/A2 and SLD is SKD11/D2, but I remember seeing at least one knife where SKD moniker turned out to be SKD11/D2.
The same is true for the "straight" SK family of steels. There's a number of variations but the makers seem to always just say SK.