Just looking through the design guide and noticed that Ian Proctor's designs seem to miss some numbers. Was there ever a Mk10, a Mk13 or 14 for example? Perhaps superstition accounts for the lack of a 13 but what about the rest?

No 13. The 10 was a one off modified 8 a river design the 14 was a dog and despite the 15 another semi-dog the 16, 17 onwards to 20, broke the domination and persuaded people to look elsewhere, such as: Jackson, Debenham & Truman, Martin Jones and so on.

At Upper Thames there was at least one Proctor Mark 8, designed to outwit Jack Holt designs on the river. I don't think that there was a Mark 10 but there was certainly a Mark 14. I believe that it wasn't a successful design (maybe Ancient Geek or Robert Harris would be able to tell more).

I used to have a book of Ian Proctor's about dinghy design.  The mk VII, though not successful, was an interesting one and led directly on to the immensely successful mk IX.  The idea was to have narrow v'd sections forwards, a fair bit of rocker in the middle, and very flat aft sections.  You dug the bows in upwind and sat at the back downwind.  The reason for the lack of success wasn't spelt out but I suspect it was a pig to handle and nosedived immediately you were round the windward mark.  I think the mk VIII was a development of the successful mk VI, which was a common shape for dinghies at the time with fuller less flared bows and a generally rounder shape than what followed.  I had a mk XV and was pleased to learn that other people thought it was a dog as I thought it was me - it was my 1st Merlin and didn't go in light winds and wasn't that stable in a blow either.

Well! The Mk 14 co-incided with my first season in the class 1961.
A number of big names had them, Mike Astley, David Peachey, John Oakley (Tony Fox.), Stuart Jardine (James Ramus.)I was doing 'O' levels and so did not get to Gorlestone, but whilst as one would expect with 'star drivers' they figured I don't recall David Thorpes daily write up in the Daily Telegraph (12 column inches, each day!)  mentioning them as race winners or top six placings overall. Two years later (1963.) the Mk 15 came along and whilst it was better especially in heavy weather it was not really a match for the mk9 though if Robin Judah had had a lighter crew who knows. David Dyer had a 15 that went well at Hamble. Robin had a mk 16 the next year but too much weight in the crew dept again! The mk 17 (1968.) was a Jackson/Jones look alike with a geometrically ssevere stern despite being sailed by David Potter (Defending double champion.) and Guy Gurney the two boats didn't really shine. (Jack Holt had a last hurrahly with a similarly sterned boat for Tom Broughton about this time but without wishing to speak ill of the dead Tom was not really a top helmsman.) The Mk 9 and derivatives really dominated with the MKs 12 and 11 doing well all round. The 12 was a very succesful all round design and the 11 a softened mk9 as the MK9 was said by John Oakley to be tricky to sail. - It wasn't but John O was always good at the mind games. It took Bob Hoare to find him out! 1968 was the last year a Proctor boat won the Championships a 9b built be Bob Hoare.