Correct! This bird is a standard 1w-male 2BXBill. The tertial pattern, and both the extent and shape of the wing-bars clearly indicate a bird in advanced body moult with retained juvenile wing feathers. The extent, shape and colouration of wingbars in L. curvirostra are extremely unlikely to ever match that shown by this example of L. leucoptera (as stated earlier by James Hanlon). See Svensson: Identification Guide to European Passerines, p. 303.
I think you have raised a very important point. You don't have to search far to find a few birds which show similarly worn greater and lesser covert bars. The Cley bird, for example, (which was a 1st summer) showed equally worn retained wing feathers and the greater coverts bar in-particular differs little, if at all from the male currently being discussed at Lynford. So, there is no doubt that this is within range and saying so I must backtrack slightly on what I have said previously about this being far to subtle to be considered in the range of Two-barred Crossbill. I simple wasn't well read enough on the subject.
Taking all that into consideration, the topic which becomes more important now is the one discussing the degree in which Common Crossbill can 'mimic' Two-barred. Perhaps poor views of of the Cley bird high in a tree and heavily cropped images would have raised the question is it, or isn't it? Luckily the bird was down to feet and world class views and huge images were retained of the bird, showing all the right structural criteria and thus no questions were raised. Brilliant.
An image of a female Common Crossbill with obvious, seemingly white more than off-white wing bars can be seen
(here). From head an bill structure, the bird in quite clearly a Common, although I am sure on the first moments of sighting such a bird the alarm bells of Two-barred must have been ringing. Maybe a flip scenario of what we have with the Lynford bird. So where is the middle ground? Structure and call. As the bird wasn't heard to call, structure is all we have to go on and a couple of blurry images of this bird are nothing like what is needed to judge it safely. Although, from the images we have the bird does seem big headed and big billed. Something we obviously don't want to see when looking at a Two-barred.
I have moved from Common Crossbill to the fence. I don't think we have enough documentation about aberrant Commons. Or at least I have seen none. But, I have spoken to more than one person who has said they have seen Common Crossbill showing this extent of wing-bar and this clean. Maybe they were Two-bars, who knows; but I think this bird either needs photographing better or more extensive field notes documenting structure and call to be 100% sure of it's correct identification.
Sorry for the rambling, it might all sound like a load of stallion stool, but I find the whole thing quite interesting and believe it should be explored much further before such comments are made pronouncing this bird a 100%, standard Two-barred Crossbill. If nothing comes from it, some of us may have learnt something at least.
