The art of the 12" company sleeve can really be quite entertaining. The middle sleeve above is not a Big Beat sleeve-- does anyone out there know what company made these? The Alicia Bridges and Travolta sleeves below are not company sleeves, but are good examples of the disco die cut promotional sleeve popular in the early years of the 12". Experiments with the 12" single format began in 1974 and by 1975 a decent amount of promo 12"s had been released. Within a couple of years the 12" single would become the format of choice for promoting dance oriented tunes. By the 80's, 12" records were pressed for most every mainstream hit, dance oriented or not. Springsteen w/ "dub version" b-sides, etc.
Above we have a couple of die cut sleeves used to market LPs, not 12"s. Below there's a Russian example. This sleeve may have been used for either LPs or 12"s, but this particular release is a disco-ish LP.