I’ve seen that Discogs link - I would argue that George Patterson Pty Ltd. is not the label as they are/were an advertising agency. There is also no catalog number.
So my thoughts are unknown artist and commissioned by Telecom Australia. Do you know what relationship the recording/work/release should have to George Patterson Pty Ltd? They were commissioned to create the work.
I think you are correct about G.P. not being the label.
I’d be easily persuaded that Telecom Australia is the label - but I have entered practically no singles and just don’t know what counts. If it was an LP or CD I’d be confident enough to use Telecom Australia.
G.P. Pty Ltd. from my reading of the cover art is both the writer of the song and also the producer.
These would be added using the Relationship Editor I think. https://musicbrainz.org/doc/How_to_Use_the_Relationship_Editor
If your cover art is the same as on Discogs then copying that over would be quicker - though if you wanted to make higher resolution scans that is even better.