As you may notice from this spec tutorial or this errata report, the two bits that serve as a "sign-status" field for BCD data show only status, not sign, for BNR data. The status codes for BNR data include a "failure warning" code; it is not necessary to signal a failure warning in the sign-status matrix of BCD data because the individual digits can be set to 1111 (four consecutive 1s) in order to indicate that the values are unreliable.
Also, when latitude and longitude are encoded to 0.1 minute in BCD format, a different BCD format than usual must be used. See the commentary in section 2.1.2 of the errata report. The positions of each digit's encoding are moved 2 bits so that the first digit has maximum value 1 instead of 7, and bits 9 and 10 are used for data.
