er, the model of LR503 'F' entered appears to have single stage Merlins ......... afaik the Mosquito B.IX had 2 stage merlins, as shown in the photo detailing the mission markings.
Does it matter?
I think that's called artistic licence. If you look closely at the model it also has a fighter nose and windscreen instead of the bomber style, but I should be surprised if more than one person in a hundred would notice that when the model is on display. At the end of the day the modeller has produced a great looking 1/24 scale diorama from what was available, I'm sure he was aware of the differences when building it, but there's not an easy way to correct them in 1/24 (I had a quick scan of the internet and couldn't find any conversion sets).