No offense, but I am struggling to make sense of this sentence.I am not sure of is if I first footfalled and then scanned a Bio on that planet if you could claim the discovery bonus by landing there next and selling the data first.
A first footfall would mean that you are definitely the first to sample these bios, as you have to be on foot to take those samples.
The 50 kCr you get if you scan a bio with your SRV's comp scanner is just a codex discovery bonus that is separate from the other payouts and is, as far as I am aware, granted no matter if you are the first to turn them in. Why else would they come as redeemable vouchers?