Hello,
the best will be to have a look
here.
If you are visiting different EU-countries you should do claim for the refund any time you are leaving the EU, so you minimize the procudures.
E. g.
You enter the EU in
Sweden
go to Denmark
fly to Switzerland
go Germany
then to Netherlands
finally to the UK
before you return to the US
As Switzerland is non-member of EU. I would do it first time in Denmark. So you get some money already back because you are leaving the EU and the customs can approve it. This money you can spend again in Germany, Netherlands and UK. And there you show all purchases you bought in this three countries before you are leaving the EU permanently.
Hope everything is clear.
Regards,
HeinBloed