To locate the correct GCDB-ID for a 1/4 section corner on an E and W boundary line take the GCDB-ID for the section corner to the west of the 1/4 corner and place a 40 in the last two digits of the prefix.
To locate the correct GCDB-ID for an 1/4 section corner on a N and S boundary line take the GCDB-ID for the section corner to the south of the 1/4 corner and place a 40 in the last two digits of the suffix.
The center 1/4 section corner gets a 40 in both the prefix and suffix of the SW section corner GCDB-ID.