Consider the example in [expr.eq] p4.6

struct B {
  int f();
};
struct L : B { };
struct R : B { };
struct D : L, R { };

int (B::*pb)() = &B::f;
int (L::*pl)() = pb;
int (R::*pr)() = pb;
int (D::*pdl)() = pl;
int (D::*pdr)() = pr;
bool x = (pdl == pdr);   

The relevant rule says

Otherwise, two pointers to members compare equal if they would refer to the same member of the same most derived object or the same subobject if indirection with a hypothetical object of the associated class type were performed, otherwise they compare unequal.

We expect that the result of pdl can clearly be that refers to D's L's instance of B, and pdr refers to D's R's instance of B, hence they don't refer to the member of the same subobject and are not equivalent. The result of the conversion is completely expressed in [conv.mem] p2. However, [conv.mem] p2 cannot well express the result in the case that multi-converts the pointer to a member to pointer to the derived classes' member. The current wording is

The result of the conversion refers to the same member as the pointer to member before the conversion took place, but it refers to the base class member as if it were a member of the derived class. The result refers to the member in D's instance of B.

[conv.mem] p2 can well tell the story that pl refers to the member in L's instance of B. However, we expect [conv.mem] p2 can also well define that pdl refers to the member in D's L's instance of B, in this case, the rule is hard to read out this meaning. The suggestion to the current wording might be:

A prvalue of type “pointer to member of B of type cv T”, where B is a class type, can be converted to a prvalue of type “pointer to member of D of type cv T”, where D is a complete class derived ([class.derived]) from B. .... The result of the conversion refers to the hypothetical member MD of class D of type cv T; any reference to MD refers to the member of M(B) of D. For class B, M(B) is defined as follows.

• If the pointed member of B is a hypothetical member that is invented for converting the prvalue of type “pointer to member of C of type cv T” to “pointer to member of B of type cv T”, M(C) of B.
• otherwise, B; the declaring-base-class.

Since the result has type “pointer to member of D of type cv T”, indirection through it with a D object is valid. The result is the same as if indirecting through the pointer to member of U that is the declaring-base-class with the base class subobject M(B) of D. The null member pointer value is converted to the null member pointer value of the destination type.

After this suggestion, the result of pdl is clear to interpret. pdl refers to the hypothetical member of class D, and such a reference results in pdl referring to the M(L) of D, where M(L) is B of L. The result of pdl is the member of B of L of D, which completely tells conversions in the path.

Not a completely formal suggestion, just one thought that can clarify the result in the conversion path.