Game not being updated via STEAM?

I installed my game via the steam platform, and once it was installed it updated.

I made sure the game said "version 9.1" and i even had the chance to select the 9.1 database when i started my new game..

However.. my brother had MAJOR problems with his installation, and so i thought i was going to be a little nice to him, and download the 9.1 patch manually for him, since he is on a slow line, and the patch is 165MB?..

i had problems with alot of injurys playing my 9.1 game, and i don't know why, but i tried installing the manually downloaded patch on my game... and it worked?? on the last few releases, i think once you updated your game with a patch... it was impossible to do it again..but now with my 9.1 patch, it worked without a problem...

so im just wondering.. are you able to install the patch multiple times this year.. or did something go wrong with my steampatch, so it didn't update properly?