... Are there any hard and fast rules on this? ...
No
.
As in many other situations in life there is not only black and white but a lot of grey
.
In recent years there has been a lot of evidence that there have been coin emissions from Greek cities which are looking perfectly Greek but have been produced under
Roman influence for
Roman needs. Is this already a
provincial coinage?
Or what about the coinages of all the client kingdoms? Or
Spanish imitations of
Roman republican coins produced because there has been a lack of small change?
What you can do is to have a look at
RPC online whether they list a coin or not:
https://rpc.ashmus.ox.ac.uk/But also this is not free from contradictions. In the introduction they write "It presents for the first time an authoritative account of the coins minted in the provinces of the empire" but list e.g. coins from client kingdoms before these have been integrated into a province. (Perhaps this has also been a step to expand the own business
area, science is not always completely neutral
.)
Regards
Altamura