You can tell the difference at a glance by looking at the wheels from the inside. As you can see, the inside view of such a wheel is practically indistinguishable from a solid black wheel. The silver (chrome) is only visible from the outside!

The model shown in the top picture is the earliest version of the 8E Mustang, on which the area around the hole on the base is NOT recessed, made in 1966. It is accompanied by the correct E type box, without a circled "R" attached to the "MATCHBOX" lettering and with "NEW MODEL" on the end flaps. There is also a version with the hole being recessed, but still with the older wheels ("black wheels with silver hubcaps", just to say it once again). That one was made in 1967 and usually came in an E type box without the circled "R" and without "NEW MODEL".

The model in this picture is from 1968 - "silver wheels with black tires", and I think there is still "PATENT PENDING" cast on the base. The accompanying box is also from 1968: E type with the circled "R". The 1969 issue of 8E had "PAT. No. 1097556" cast on the base. As you probably know, it came in either white or orange-red, and it was usually packed in one of three different F type boxes which are all fairly scarce. Therefore you can also find the 1969 version in a 1968-style E type box.