In the first Avengers movie, Tony hacks into SHIELD's computers while onboard the helicarrier by placing a device of some sort on the command terminals used by Nick Fury on the bridge.
Later when Tony, Bruce, and Steve are in the lab working on a way to locate the Tesseract, Tony tells Steve that Jarvis is currently hacking SHIELD's computers and, "In a few hours, I will know every dirty secret SHIELD has tried to hide."
It is safe to assume that this information would have included data on both the history of the Tesseract and Dr. Pym.
It is reasonable to assume that before starting the mission to travel back in time that Tony, Steve, and the rest of the team would have reviewed all of this information looking for places in time where they could locate the infinity stones.
This piece of information, in particular, might have piqued their interest and drawn their attention as it involved; one of the items they were looking for, a place Steve was very familiar with, a place Tony's dad worked, and the Pym particles they were using to execute the time travel plan.
It might even have been on the list of possible times and places to get the space stone but was ruled out as there was a better opportunity to get three stones at one time during the battle of New York.
The fact that Scott Lang doesn't seem to know about this alternative time and location while Tony and Steve do, is a brilliant use of the character driving plot. Tony and Steve are both detailed oriented and would have read the briefings in-depth and committed them to memory. Scott on the other hand, well he's been established as a bit of a slacker and probably would not have read all of the briefing data.