Describing a horse by its sire/dam name - when?

[EQUIDAE]

When you see and ad for a horse and it is describes as say, an Amiro Z mare. How far back in the breeding does it go or does it mean that that is the actual sire?

Sorry for the numpty question...

 

[Spiderman]

If she is described as an Amiro Z mare, I would expect her sire to be Amiro Z.