You may need to be more descriptive to find the answer(s) you're looking for. If you are referring to Oracle Cloud Infrastructure Classic (OCI-C), formerly referred to as Oracle Public Cloud; this is Oracle's first generation public cloud offering and continues to provide various infrastructure and platform cloud services. Oracle's next generation public cloud, Oracle Cloud Infrastructure (OCI) provides an even more redundant, scale-able and high-performing architecture. The classic, OCI-C, documentation can be found under the links for services with "Classic" in their name on the following site: https://docs.oracle.com/en/cloud/iaas/index.html
Hope that helps.
I agree with Kasey. There is no such thing as regional classic. There is OCI and OCI classic each of which is deployed in different regions. For classic we have Slough and Amsterdam in EMEA. I think you have got your concepts mixed up here.
You can look up per service the datacenter location using this link:
Any service NOT starting with "Oracle Cloud infrastrucure" you can consider is a classic service.
The classic services indicate single datacenters. While OCI represents 3 datacenters. So for EMEA "Frankfurt" and "London" are for OCI 3x Datacenters. Amsterdam, which only hosts classic services is a single data center.
Actually Regional OCI-C was originally planned, and the more recent OCI-C locations have some extra features compared with the original Slough and Amsterdam. OCI-C GBCOM-SOUTH-1 in the London area is an example of that. Few "regional" documentation references remain now in the OCI-C doc but you can see region support mentioned multiple times in this for example:
So I expect that is why the OP was referring to regional OCI-C