Based on the above description, that would explain how Manhattan and the Bronx ended up with the same Borough Preliminary Signal- 6-6. And they ended up with non-overlapping box numbers.
On another thread, I noted that in 1945 Rescue 3 appeared to respond to boxes in the 12th Battalion. R3 other responses in Manhattan required a special call or a multiple alarm signal.
So, the question arises; how were the 12th Battalion boxes received on 143rd Street? Was it via the Manhattan-Bronx Interboro circuit? To the firehouse or to the Bronx CO (which re-transmitted the box borough wide)? A phone call?...Manhattan to R3, Manhattan to Bronx CO to R3?
The master telegraph key in the Manhattan CO had a selector switch that divided the Borough into three sectors, or combinations of two sectors (or all sectors). Except for All Hands or Multiple Alarms, most telegraph signals in the Borough were received by only a limited number of firehouses. Was R3 on the uptown sector?