All Tbreds are unlocked, I asked many xp2200 owners when they first got their chips to confirm it and they all said its true. The L1s are connected and it can be confirmed via testing with an ohm meter (they are connected below the surface of the chip).
The connecting of the 5th L3 bridge is simply to use the lower multis, the kt400 chipset allows you to use both the high and low multis but if you dont have one you have to make the change manually.
All chips from xp2000 and down can only access the multis from 5 to 12.5(when unlocked), all chips from xp2100 and up can only use 13 and up (12.5 and 13 is the same multi depending on how the 5th L3 on tbred or L10s on pallys isconnected) unless you modify the L10s (pally) or L3 (tbred).
So all of the chips from xp2200 and up can access all of the multis from 13 up without modifying the bridges, you only need to connect the 5th L3 to access 12.5 and down.
markodude thats why you are getting 12.5x on the 13 multi, if you want the higher ones just undo the 5th L3.