我不知道各个公司是如何组织的。

There are many ways a company could organize themselves.  

Delaware LLC at least has to reigster in your state as a foreign corporation to be able to do business. 

Some other time Delaware LLC could just create a new LLC in a particular state as subsidiary.   Sometimes it's not for liability isolation but for tax purposes.  

I am not sure what is your concern.  You buy a house you have title insurance.  If you are buying a bank owned property and this bank is in Delaware, you thinking about suing the bank?   

That's above my pay grade.  I am not in the business law specialty.