"But what does the reference to the letter mean?"
His reference to the subway could mean that he used it himself, and had picked up the cab from the nearest station.
The reference to 'one in white' meant the Mother Confessor.
It is, however, disputable whether such biblical references mean a common practice or just onetime events.
The reference to the Night Express meant an arrival, not a departure.
He's trusting that you know what these references mean.
The reference to the wind means that the virus would cover only four miles of land and then be blown out over the sea.
I no longer know what the texts, references, footnotes and traps mean.
The reference to the sidelined players meant the next three men in succession were taken too.
Does his good reference mean that you can trust me, too?