I have seen the future and it stinks.
I live in NV. Any car registered as newer than a 1965 is tested each year. The licensed test stations are electronically hooked into the DMV. Each car is tested against emissions standards for the year of registration. It is difficult for a stock air-cooled VW to pass the emissions tests. If you have a modified air-cooled VW it takes a miracle. (I know a miracle worker!)
Fortunately, I own a 1964 VW Speedster. I know that there is no such thing, but I gots the registration babeee! I do not have to be tested each year. I have to pay $39 in license fees each year. Of course, there is a catch. Yes, my 1964 VW Speedster is a 1964 VW for insurance purposes. Thus, I have to pay the going rate for 1964 VW insurance (cheap).
My advice for builders is to obtain an early VW pan and have it restored (even updated to IRS) with the original VIN. Have it licensed as an early VW. (You may have to go hand-to-hand with the DMV over this. If the DMV clerk will not play ball; walk. There is always another day and another DMV clerk.) Once you get the car registered, you are home free. (Always carry copies of the various legal documetns in the car for the fuzz who did not get the word.)
If worse comes to worse, register the car in another state. A car registrered in any state is registered in all states; that is the law. Once again, you might have to go hand-to-hand with the DMV, but it is worth it.
It is, at least in NV the chassis year that determines the registration year. The engine year is unimportant.