Traditionally, from Midland Railway days, services on the Tottenham and Hampstead Joint line - which became the west end of the Goblin - were through to Moorgate via the Metropolitan Widened Lines, with pre-WW1, some to Victoria via the LCDR, eastern temini varying - some went on to Barking, most didn't go that far, and formed the bulk of the Midland's London suburban services. AIUI, they were badly affected in the Edwardian era by the opening of the 'Hampstead Tube' (later Northern line), and the electric trams. Service through to Moorgate was withdrawn in 1940 due to war damage, and, unlike the 'main line', never reinstated post war, with most services only going to Kentish Town. And in the post war period, until the 1980s (?) such orbital services (as it was, not running beyond Kentish Town) were the cinderellas of London's transport system, neglected investment wise, and infrequent services. When, under the GLC, they developed, it was as orbital services - so 'Goblin' went to Gospel Oak, to change to the North London line, the curve to Kentish Town having gone and the sort of frequent service to justify restoring it seen (rightly or wrongly) as too difficult, and demanding of paths over what had become Thameslink.