Oliver Smith has posted on the official WWIIOL Battleground Europe forums a clarification about depot impact on brigade movement.

In order to manually move a brigade across a link:

• You must 'own' and 'control' the destination city (see /own command),
• You must be the current owner of the depots at both ends of the link,
• If there is a firebase on the link, it must not be enemy owned.

This movement rule does not affect /fallback or the automatic retreat of brigades. Again: brigade routing is *not* affected by this new rule, only the manual movement of brigades by OICs and HCs.