Peter Duniho wrote

Under what rule was that pilot allowed to fly solo without the
necessary category and class rating? On what Student Pilot
certificate did you make the required solo endorsement?

Not the same situation, but......

(k) Exceptions.

(2) The rating limitations of this section do not apply to—

(i) An applicant when taking a practical test given by an examiner;

(ii) The holder of a student pilot certificate;

(iii) The holder of a pilot certificate when operating an aircraft under
the authority of—

(A) A provisional type certificate; or

(B) An experimental certificate, unless the operation involves carrying
a passenger;


If one builds a homebuilt twin, he does not need a MEL Certificate
in order to fly it solo.

However, if it is a homebuilt tailwheel airplane, he must have the
tailwheel endorsement because by being a "additional training
requirement" instead of a "rating requirement" it is not waived by
k(iii)(B)

Bob Moore