It's... literally a retcon.

What was shown (i.e., what was described to the players) originally is being amended to include a blockading procedure. This sort of thing happens all the time in a roleplaying game when players/GM forget to mention something or have differing assumptions about what is happening. You can't now use the original images/descriptions to complain about it not making sense, since events now didn't happen exactly the way they were presented.