Bolero, that's correct. A debutante in Great Britain did not have to attend finishing school; and the completion of finishing school had little to do with whether she could be presented at court.
She had to be sponsored by a woman who had also been presented at court. Her mother, an aunt, grandmother, mother-in-law, or friend of the family (though that was more rare). There were specific dresses that had to be worn, the requirements of which were published ahead of time.
This is true for men as well, they also had to be sponsored by a man who had been presented.
Everything you ever wanted to know about
Dress and Insignia Worn at His Majesty's Court, Issued with the Authority of the Lord Chamberlain (1921) from the Internet Archive.
This includes the dress of Members of the Indian Civil Service (who were often British, not Indian) in the Diplomatic Corps. Though it does say:
In the case of Indian gentlemen ... a pugree may be substituted for the (headgear) prescribed in the rules.
That book is entirely filled with requirements for any possible man, in whatever role down to His Majesty's Swan Keeper, attending any possible Court event. There's a page on what women should wear.
Feathers, veils and trains have now been abolished, and the style of dress for ladies attending Courts is the same as they would wear at any official evening reception, with Jewels, Full-size Orders, Decorations and Medals (see pages 107 - 109).
This book is full of drawings of what men must wear to court. For women it says:
Sketches showing the style of dress expected are on view at the Ceremonial Office, St. James's Palace.
Probably because what men wear is the same for every given rank but women can wear a variety of different dresses, provided they meet the style expected.