  In this work, we study the impact of imperfect sharing of the Channel State
Information (CSI) available at the transmitters on a Network MIMO setting in
which a set of $M$ transmit antennas, possibly not co-located, jointly serve
two multi-antenna users endowed with $N_1$ and $N_2$ antennas, respectively. We
consider the case where only a subset of $k$ transmit antennas have access to
perfect CSI, whereas the other $M-k$ transmit antennas have only access to
finite precision CSI. The analysis of this configuration aims to answer the
question of how much an extra informed antenna can help. We model this scenario
as a Decentralized MIMO Broadcast Channel (BC) and characterize the
Degrees-of-Freedom (DoF) region, showing that only $k=\max(N_1,N_2)$ antennas
with perfect CSI are needed to achieve the DoF of the conventional BC with
ubiquitous perfect CSI. Furthermore, we identify the increase of DoF obtained
by providing CSI to an extra transmit antenna.
