William Heinemann reprinted DARK OF THE SUN numerous times: in 1965 (same year as the first printing), 1972, 1975, 1978, 1983, 1984, 1986, 1987, 1988, and 1989 for a Uniform Edition.
Notice the contrast between the two spines, one of which has age-darkened. It is very uncommon to find a copy with bright white "Wilbur Smith" on the spine.
Below, another copy signed in the same green ink as my copy above, but the copy below is not mine.
I once owned almost all of the Heinemann printings, but sold off all of the reprints
I have owned and sold a number of signed copies of DARK OF THE SUN. All below are first printings, except the last one designated as a 1984 printing.
Wilbur used a very sloppy signature for a short while, then basically stopped signing books for collectors and fans.
1984 reprint
The Viking Press never reprinted its first edition or published any later editions, so all copies are first printings of the first edition.