The code before the fix only checked the length of R value of the last
signature in the loop, and only for equality (but the length can be
less than 32)
The fixed code checks that length of the R value is less than or equal
to 32 on each iteration of the loop
The BOOST_CHECK(sig.size() <= 70) is merged with sig[3] <= 32 check,
and BOOST_CHECKs are moved outside the loop, for efficiency
As described in "Key origin identification" section, a descriptor
that has hardened derivation after xpub does not let you compute scripts
without access to the corresponding private keys. Such a descriptor is
practically useless.
The text after the descriptor said "with child key *1'/2* of the
specified xpub", and clearly an xpub cannot have "child key" with
hardened derivation. Therefore it makes sense to fix this inconsistency
to not confuse the reader of the doc
Dmitry Petukhov