What is the authenticity of taking the Hadith to mean that the intended types of dogs are specific ones, such as German Shepherds and the like, and not undesirable dogs?

We do not fully understand the intent [of the question]. The Hadith is clear in prohibiting the keeping of any type of dog except for the needs mentioned therein, such as hunting or guarding livestock. If it is permissible to keep them for these needs, then it is permissible for any type of dog. Thus, the prohibition or permissibility is related to the presence or absence of a legitimate Shariah-compliant need.