How was warning the countryside a collective effort in Paul Revere's Ride?

When correspondence is so easy in today's world, it is
hard to believe the amount of effort and planning it took to communicate during the
Revolutionary War. Paul Revere, who was living in Boston, was a member of the Committee
of Safety as an express rider to carry news and messages as far away as New York and
Philadelphia. On the evening of April 18,1775, Dr. Joseph Warren instructed  Revere and
William Dawes to ride to Lexington and Concord and warn the leaders that the British
troops were moving in their direction with the objective of arresting Samuel Adams and
John Hancock.  They were not worried about military supplies since they had already
moved them out of Concord and knew they were safe. Revere and Dawes were sent out to
warn the leaders in Lexington and alert the militias in the nearby
towns.

Revere, who was afraid that they wouldn't allow him
to leave Boston,  had already set up a warning system with the deacon of the Old North
Church,Deacon Robert Norton, to send a lantern signal to the colonists of Charleston. 
After he rowed across to Charleston, an activity that was illegal and could have gotten
him arrested, Revere verified with the Sons of Liberty in Charleston that they had
received the message of two lanterns, the British were coming by sea.
Charleston residents then dispatched  more riders to the
north.

 Revere warned patriots in Somerset and Medford, and
then many of those warned set out to warn others. He arrived in Lexington, where Adams
and Hancock were staying with Hancock's relatives.  There he was joined by William
Dawes, who had done the same thing but followed a different route. The Lexington militia
then dispatched riders to the surrounding towns.  By the end of the night, possibly
forty riders were involved in the spreading of news.

Revere
and Dawes decided to continue on to Concord.  They were joined in Lexington by Dr.
Samuel Prescott, who was returning to Concord.

So, we have
forty riders, the Committee on Safety,  the Son's of Liberty in Charleston, the Deacon
of the Old North Church, and the three men credited with this ride: Paul Revere, William
Dawes, and Dr. Samuel Prescott.