You maybe correct. In their current parts lists and instructions they do not show or mention the slide valve.
So if you take it apart and lose one of the slide valve parts, there aren't any parts you can order from them now. They might still have some slide valve parts though, if anyone that works there now knows about it. it is a pretty obscure feature. I haven't ordered a current version Perry Pump carb so I can't say for sure if they quit doing it or not. My example carbs are all older models. This may be a feature from way back in the old .60 engine powered pattern planes era.