RECORDS
I don't know if Procaudio counts as an actual label, but from 1965 into the early '70s Procaudio Ltd appears to have produced records for other companies, presumably for sale or distribution by them. Numbering was in the PC-000s, with both sides of a record having their own discrete number. On the few examples I have seen the only reference to Procaudio has been on the sleeves, not the labels; the PC-000 numbering is the thing to look out for. The first example above, 'Animal Sounds - Mammals', with an introduction by Peter Scott, was made for Purnell's Encyclopedia of Animal Life and the Macdonald Junior Reference Library. The numbers on the labels, PC-043 / PC-044, seem to be the matrix numbers; according to the record's sleeve its catalogue number is 356-03257-4, which means absolutely nothing to me. Apparently it was part of a series which came out in 1970. I have seen 'Animal Sounds - Insects' listed; the introduction to that record was provided by Dr. Maurice Burton. The second example was made for Double-S Productions. Other labels with a PC-000 number were Craigie College Language Project and Career. Some others. The company was resposible for producing flexi-discs as well as vinyl ones. Thanks to Robert Lyons For The Info.
