In last week's post, Acknowledging an Important Source, I noted the importance of Gelo's book 'Chess World Championships' as a reference for many of the pre-1883 pages on my site. The book is documented by a six-page bibliography including an entry for:-
Loewenthal, J., ed. The Chess Congress of 1862. London, 1889.
A digital copy of the book is available online via a Google Books page, The Chess Congress of 1862, subtitled, 'A Collection of the Games played, and a Selection of the Problems sent in for Competition. To which is prefixed an Account of the Proceedings and a Memoir of the British Chess Association. By G. W. Medley'. This book is undoubtedly the source for much that is known about the event.
Wikipedia has a page, London 1862 chess tournament, that dates back to October 2008. Its source was London 5°Congresso Britannico, 16/6 - 2/8 1862 (archive.org // xoomer.alice.it). Both references use the same technique to indicate draws that were replayed, and neither shows which games were forfeits.
The most recent incarnation of the event is probably on the Zanchess blog: London 1862 – Preliminary results and xtabs (January 2016; 'There were 91 decisive games, of which 21 were forfeits; two decisive games are missing.'; see comments, esp. 'ckr') and London Chess Congress 1862 – a first-look look (February 2018). The forfeited games are not indicated here either.
If the forfeited games were handled as they are in modern times, Loewenthal's record in the event would be excluded. He scored +3-0 (+1F-9F) for a total of 10 forfeits out of 13 games.