I am kind of confused by this whole thing. I live in Texas and have 5 vehicles insured with JC Taylor. My other vehicles are company vehicles, but my wife and I own the company. Belonging to an organization like the ATHS helps getting insurance. Actually, in Texas, if a vehicle has antique license it is not required to have insurance. However, I would never back out of the drive way without liability insurance. Unless a driver or a class of drivers, such as age, is excluded, insurance companies have to pay a claim. Although Grundy is a surplus lines insurer in Texas, they are still regulated by the TDI. Unless you are specifically excluded because of your age or driving record, you would be covered. This is another one of those situations where I would not rely on hearsay. I would call this agency's help line.
http://www.tdi.texas.gov/webinfo/contactus.html They are getting paid Texas dollars to help consumers.