I note that Spanish infantry in the Spanish list are Ex Javelin,-, ME,
but Spanish mercenaries in the Syracusan list are -,Impact weapon, -.
Curious about the reason for this difference.
The Spanish you refer to are specifically Lusitanians who have their own list. More "generic" Iberians which have Impact weapon have a different list. So unless the mercenaries were Lusitanians they won't get their classification.