I can see the lip/recessed tank top on all those photos - except Boxhill, where I'm not sure.
Look at the base of the tank filler, for example. You can see the skirt/lip at the bottom of it, and fixing bolts at the front, but not on the edge that coincides with the tank side - because it is below the top edge. Same with the circular plate bolted onto the tank top at the front of each - it has an obvious thickness front on but appears flush with the tank side.
And with the preserved 32678, the tank side cladding (renewed?) has a longer overlap onto the tank tops, so much so that the filler cap has had to be be rebated into it. You can see the curve with its line of bolts.