This article is from the Friends FAQ, by Andy J. Williams AndyJW@dartmouth.edu with numerous contributions by others.
JG: "We knew there was going to be a Phoebe/Ursula story [See 4.3] from the
get-go. In the case of Paolo, we started that "arc" without knowing exactly
where or when it would end up -- the decision to have him make a pass at
Phoebe [112] was actually arrived at pretty late in the game. However, an
upcoming two-part arc involving Rachel, Barry [Rachel's ex-fiancé and Mindy
[Rachel's Bridesmaid & Barry's girlfriend]] was conceived of all at once.
"To answer your initial question, then... it varies. "
 
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