Jeff Chan wrote:
Draft documents notwithstanding, in actual practice most blacklists use only the fourth octet. A few vary the second and third octets, but they are exceptional.
OPM was an exception, with a magic "1" as second octet.
I never found out if that is a "version number" for the specification of the remaining 16 bits, just a trick to avoid 127.0.0.0/31, or something else.
"Extend to 16 bits" is a straight forward idea, and one Jeff Chan proposed it on this list some years ago... :-)
IIRC the "isipp" codes (mostly white lists) use rather convoluted 127/8 meanings.
Frank