It depends.......on where the lots are located what county and city.
For instance in Cherokee County we have a website and advanced computer system to record deeds.So recordings show up pretty fast from the sale in the courthouse records.Other Ga counties still use archaic manual recording systems that don't show up ownership changes for months and months.
It could be that they purchased from the owners or simply put them all under an option contract for a certain price and then resale to you.
I am doing this right now on an assemblage deal.I get the parcels under contract the cheaper the better and then the developer pays me xx number of dollars.Example i get the seller to sell to me for 50k a half acre the developer pays me 100k so i profit 50k on each parcel.