First let me say a nice improvement on the copy from Slot Cliif!
After I have placed a Stockpile and defined what parts it will hold, if I delete a part from the Supply Stockpile window the part disappears from the stockpile immediately.
What happens to these parts?
In the picture below where did my (Already paid for) Axles go?
I did not receive any refund, will the first 18 Axles ordered next time be Free?
Just a thought? 
You never used to get a refund, but this changed in the latest version, although there is a chance I missed the refunds in the case of supply stockpile changes. I’ll look into it.
Kind of a related noob question so don’t want to start a new thread for it. Is it by design that you don’t get any refund when you delete a station or conveyor with a Work-in-Progress vehicle on it?
Thanks Cliff.
Considering this:
Would it not be more ‘natural’ if you delete a part from the requester window that those parts stay in the stockpile.
I guess then you would have the problem that they wouldn’t be used and take up space if no other slot requested the parts that was linked to the stockpile.
When you ‘Order’ the parts by adding them to the stockpile they don’t just ‘appear’ they arrive by resource conveyor.
Would be nice to see those parts that are ‘deleted’ go back on the resource conveyor and back to the import slot.
If I am getting a refund I’m sure the manufacturer would want them back 
I guess the importer also becomes a ‘requester’ in this case and could get complicated.
Yup, if importers start becoming exporters too, I fear that the ode may collapse under its own complexity 
The reason they do not hang around is they, as you suggested, take up space and may NEVER be used. For example, if you upgrade from aircon to climate control for every car model, you will be blocking those stockpile slots until the end of the game, which would be disastrous for efficiency.
Regarding losing a car when deleting a piece of conveyor. Its currently in there like that just because its easier, and I haven’t coded a way to deal with it. I admit that this is a bit of a ‘bodge’ and that I need a proper solution, maybe refunding the cost of all of the components (at a minimum?) that went into the car would make sense. Any other option, such as pinging it to the next empty conveyor tile, is fraught with complications and bugs.
A way around losing the car may be adding in the option to stop each slot. Just a thought, so you can pause a slot, holding up the line from that point to purge the units in the way. Just a thought.
I would also like to see a way to stop the line at a particular conveyor. This would make re-tooling the line without losing a bunch of production much more practical than it is.