Problems moving Age of Empires 2 files, having to download half the game again.

Hello,

I just bought a second copy of AoE 2 on a secondary steam account for friends who come over and want to play. Instead of re-downloading all 4+ GB of the game files again on my terrible internet I decided to copy/paste the steamapps/common/Age2HD folder to the new computer.

When I went to install the game in Steam, it discovered all the files and then gave me the blue "Play" button to show that it was ready to go, but then queued up 2.3 GB of "updates" to download. Is this a normal thing to have happen? The game is up to date on my main PC and now steam wants me to download an update that's half the size of the game on my 2nd PC?

If this is normal I'm fine waiting but it seems odd to me. Thanks.