The Manifesting Generator is the type whose status varies between accounts of Human Design, and that variation is a fact about the system worth recording.
A type, or a variety
Some presentations of Human Design count five types and list this one among them. Others count four, treating this configuration as a variety of Generator rather than a category in its own right, on the grounds that it shares the Generator's defining feature and adds a further one.
Both counts are in circulation, in material produced within the system rather than by critics of it. This atlas records five, which is the more common arrangement, and records here that the number is not settled.
Why the ambiguity exists
The types are read off a pattern of defined and open centres in a calculated chart. A classification derived that way can be cut at more than one place, and where it is cut is a decision rather than a discovery. A system whose categories emerge from a mechanical rule will always face this question, and how it is answered tells you about the presenters rather than about the rule.
The wider point
None of the four systems Human Design draws on, the I Ching, astrology, the chakra model or the Tree of Life, contains this typology. It was introduced by Ra Uru Hu in 1987, and no independent evidence establishes that people sorted by it differ as the system says. The atlas records it as the system's own model.