That is what I believe too. Sami stated in the manual that e.g. Singapore and HongKong are not able to open further bases, but in the next paragraph he included that this will change over time, as in case of Latvija joining the EU later.
Btw, what happens, if i start in Latvija as part of the Soviet Union and open bases in Leningrad (St. Petersburg) e.g. Then Latvija joins the EU and I open a base in Berlin. Will the St. Petersburg (Leningrad) base then become invalid?