First Mapped and not First Discovered pays you 8 times the base value.for some reason, mapping stuff you previously scanned earns more than discovering & mapping something new. FD & FM an ELW pays ~3.3 mil whilst FM an ELW you've previously scanned nets more like 5 mil.
First Mapped and First Discovered pays you 3.7 times the base value but then that is included in the value multiplied by 2.6 for the separately reported FD bonus giving you 9.6 times the base value in total for both.
Mapping an already mapped gives you the base value times 3.33.
It's just reported misleadingly, you do get more credits for first mapped and first discovered.