@alienik Technically yes it is. GWR class 4500 was the first design and a further batch of 100 were built in 1927-29 (4575 - 5574) these are often referred to as GWR class 4575 in certain publications as they differed from the original batch (class 4500) in having larger capacity water tanks. I guess its a sub class of the 4500's but can be viewed as a class in its own right.
In which case it does need to be moved to the sub class 4575 gallery. I have tried to edit the caption details uploaded but can't remove 4500 for some reason and replace it with 4575.