The problem is not how the Company located, the question in the treaty is that it clearly defined "State" actor and it did not declare the treaty would also be including "Non-State" actor.
Let's recap that part.
Resolution 2222 (XXI)
Outer Space Treaty
resolution 1962 (XVIII)
Legal Principles
Technically speaking, had ISIS have a space program, they can fly into the moon and extract any material and they are not bounded by the Outer Space Treaty, the treaty only applies to the member of the state that sign into it.
The reason behind this "Grey-Area" can be only be that the treaty is quite old and they were not designed where a time space travel felt into commercial category. The exclusion of non-state party (Which acknowledged on point 5 of resolution 1962) which declared
Which bounded only national activities put forth for non-governmental bodies, but did not bound the non-national activities (as Private Company does not represent that nation) into the treaty. Hence, the treaty does not limit commercial space flight, only activities of state actor (or national activities as said in the treaty)
Another reason is that company can register their business registration basically every now. And it would be quite easy for a company to register in a location that did not sign this treaty and for further appropriation of the space, which would have by passed the treaty anyway. Hence I guess this is the reason why this law has not been amended.
Simply saying Virgin Atlantic would simply registered themselves in Malta by opening up an office there and base every paperwork off from Malta while every launch work and physical work still base out of the US, and Malta is not a party signed into this treaty, and thus, this bit could technically negate the treaty even if the treaty is amended to include non-state actor
As I said, this is actually a fair deal, anyone can have a space program, simply they were opened to everyone but the government, and if Chinese Company magnate like Jack Ma or Li Ka-Shing want to have a go with the space, they are more than welcome for it too.