A very long time ago, Leaders were restricted to giving information
only from La Leche League resources, but then again a very long time ago,
La Leche League pretty much was the only resource.  Thankfully, things
have changed for the better in the intervening years.
     It is my understanding that a Leader may provide a mother any
generally accepted referenced information.  As a Leader (and even as an
IBCLC), I always start with my LLL resources: Womanly Art, Breastfeeding
Answer book,Leavens, New Beginnings, etc, then I go to my professional
texts: Lawrence, Riordan & Auerbach, etc.  If I could not find the info
in those sources or if I did not have those sources, then I would check
with the APL dept (who does have those sources, and more), I might also
check Lactnet sources (starting with the archives).
   Especially as a new Leader I think checking as many sources as you
have available to you first is part of the learning experience, and the
APL dept is there also to help you learn.
   For me the key is the reference.  Whether I am giving a mother
information as a Leader or as an IBCLC, I reference it.  In fact, if it's
over the phone, I tend to 'read them from the book', including book
title, authors, chapter & page number.  Even tho after doing this for 2
decades some of the information is seared into my brain, I find it
reassures the mother that this information is printed somewhere, and it
covers my tail - which is one of the few things I remember from my AF
basic training about a thousand years ago: CYA (Cover your - uh, ahem,
tail!)
   As an IBCLC, I have frequently been known to pick up a book open it to
a specific section and refer to it when I'm rapping up a consult, so the
mother knows I didn't just invent the information I'm providing.
     I'm also clear about whether the information I'm providing is from a
study or whether it's anecdotal evidence  from either a mother or an LC,
or whatever.
Hope this is helpful.
Kathe Catone