My position is the figure list the dimensions as minimum and does not prohibit the use of extension tabs. The interpretation provided says they are acceptable. End of story. What is more economical in terms of time and cost? In the absence of more definition by the customer/owner, go with the less expensive method, i.e., longer test plates or extension tabs.
NYDOT specified the plates must be 5 inches in length, no extension tabs permitted, and the entire 5 inches must pass VT. But, most people that have worked with NYDOT understand NY is a world unto themselves.
Just my opinion.
Al