Most of the updates were made during the production of the cars and not "aligned" on model year boundries. It is therefore difficult to differentiate model years in the traditional "Detroit" sense. You can either think of the car as having a single model year with numerous production fixes, or you can take note of the updates made to a particular model year.
Minimizing model year changes was one of the aspects involved in producing the "ethical" sports car. John Z. DeLorean felt that a lot of the model year changes were introduced not as genuine improvements to the car, but as styling changes to make the previous models obsolete.
The list of model year changes and production fixes are listed in detail in this page here.
The DeLorean fuel tank is located in the front wishbone of the chassis, behind the suspension cross member and underneath the luggage compartment. The first cars had two indented lines running lengthwise and a small flap in the hood that allowed the owner to fill the tank without opening the trunk. Since the gas flap did not lock, a locking gas cap keyed to the ignition key was included.
The stamping process used on the stainless steel body panels of the DeLorean is more difficult than the carbon steel of most car bodies. In an effort to cut costs, the gas flap and it's hinged assembly were discontinued, but the two style lines remained.
The existing stock of locking gas caps was continued until it was exhausted. This created a few cars without the the gas flap, but with the locking gas cap. Later, a non locking gas cap was substituted. The underside of the hood always remained the same. The raised lip contacts a gasket on the underside of the hood, sealing the gas cap area from the inside of the trunk.
Unfortunately, even the two relief lines proved troublesome. Stainless steel just does not confrom as easily as carbon steel, so an unacceptable number of hoods were cracking while being stamped. The third version of the DeLorean hood is totally flat, with neither gas flap or relief lines. This style clearly identifies all '83 DeLoreans.
Unique to the third variety of hoods, a raised "DeLorean" nameplate was attached to the front on the driver's side. New hoods, from the original factory stock, are of this style but without the nameplate.