RCA
RCA Victor Records went in the mid-40s to a complex system, in which all records had a 2-digit prefix denoting the type of music and a 4-digit specific number. Most popular 78s had the prefix 20, but other prefixes existed.
When the 45 rpm record was originated in the late 1940s, a prefix was set up for each type of music, with 47- for the popular records whose 78 rpm version was given a 20- prefix and 48- for the country records whose 78 rpm version was given a 21- prefix. At first the numbers of the two versions were not similar, but in 1950 the system was changed to provide the same numbers after the hyphen for both speed versions of a single record.
As the 1950s proceeded, most prefixes other than 20- for 78s and 47- for 45s were eliminated, except for subsidiary labels. And of course, RCA finally phased out production of 78s in the U.S. by the fall of 1958
In 1969, a new prefix, 74- was introduced for stereo 45s, starting with 74-0100. Although it has been asserted that this series was primarily for rock acts, several of the earliest 74- issues are in fact by easy listening and country performers. RCA issued singles in both series until the 47- series became 48-1000 after issue 47-9999 in 1971. The 74- series continued into 1973 when it was replaced by an APB0- series, again with low four-digit numbers after the hyphen. This series was short-lived; in 1974 the prefix was changed to PB- (and sometimes GB-), with numbers starting at 10000. During the BMG era, the mid-1980s, various series were used – 5000-5100s (1984), 8600s (1988)- and 2500s (1990). The 62000 series began in 1991.
Read more about this topic: Catalog Numbering Systems For Single Records