I noticed that it is patched to the 1.3.8 version.

Wasn't version 1.3.7 the last official patch?

Is the "Titanium Update" included? Or will installing that just create problems?

NOTE :

Yes, I bought the boxed / retail version some time ago and registered to get the "Titanium Update".

I still have it, the last official patch ( v 1.3.7 ), the unofficial patch ( v 1.3.8 ), and the "Titanium Update".

The code given at activation no longer works because of changed hardware.

1.3.8 is the last official patch.
It grants compatibility with certain mods, fixes anti-missile weapons and adds the IEO Reba 8.3 v14 as a default game mode. (Use that mode for multiplayer)