In the context of the other coins minted during the revolt and siege of the 1st century, it is not surprising that the depiction of the species is less photographic of "full sets" and more representative of the mitzva and of the holiday. The symbol may have been an act of rebellion in itself, bringing distinctly Jewish practice, whose restoration they were trying to achieve, to the fore. This would be in keeping with the Jewish patriotic slogans adorning these same coins.
For other examples of the symbolic 4 species images on these coins, see this survey of the coins of that period and their meanings, particularly
- 2 lulavim (bundles?) and an esrog (p. 130)
- a palm tree (p. 130)
- 2 lulavim (bundles?) alone (p. 130)
- a lone esrog (p. 130)
- a lulav bundle and an esrog (p. 134)
- a lulav (bundle?) and 2 esrogim (p. 136)
- a lulav bundle and and esrog (p. 138)
- a lone lulav (p. 138)
- a nisuch hamayim jug and arava (p. 139)