May-be some trim parts are different (like 68 had a lower 'rocker moulding, or "Chevy II" emblem) that was attached (partly) on the lower edge of the fender.
Same fenders "basicly - 68 - to - 72 [ other than some trim parts or
"side marker lights / engine size numbers ] ===== the basic fenders all interchange (just different trim / head-light trim, moulding trim, name plates) ....
the 68 Nova .... still used both the "Chevy II & Nova names" ; starting in 69 --- they dropped the "Chevy II" ==== from then they were just
' NOVA '
Meaning - that they used many different side marker lights .
A plain jane car had a small simple side light ( with JUST the light ).
Then the 'up-scale' models had the side light AND engine (size) numbers, which made the 'Whole assmebly larger' .
Alot depends on which way / what you want to have on your fender.
If you have the 'small light' === then , the larger light should "cover that hole" by using the the light / engine number type side light ....... get it .
Then, some people 'cover over that hole , and use No side light'
Here is the "plain jane" -- "small side light" ; .... click on top bar to 'enlarge' -- both pictures ...
and, a 74 --- that he "patched over his side marker lights" ;
68-69 are the same fender only difference is ornamental like marker light with engine size the original 68 were blank where engine size was and a thin metal foil sticker was applied to match engine size and 69 had the bezel that was completely metal with engine size as part of it and 68 was white light and 69 was amber not a big difference if you're not trying to be own correct.