Section 2.4 (SubMgrs) says this
--
It can address the same Web service (Address and ReferenceParameters) as the event source itself, or it can address some other Web service to which the event source has delegated management of this subscription; however, the full subscription manager EPR (Address and Reference Parameters) must be unique for each subscription. 
--

how a subscription manager determines one subscription from another is
an impl choice.  While normally its true that the EPR (addr/refP) will be 
used to do this, its also possible that someone could setup a system where
there is only one Subscription per user and therefore uniqueness can be
determined by something other than the SubMgr EPR - ie. the userID.

Proposal:
Remove the last part of the sentence:
"however, the full subscription manager EPR (Address and Reference Parameters) must be unique for each subscription. "

as its too restrictive and how its done is an impl choice - we don't need to
mandate it.

resolved on 2010-01-05 with:

remove: however, the full subscription manager EPR (Address and Reference Parameters) must be unique for each subscription. "

and

In some cases, it is convenient for all EPRs issued by a single event source to address a single Web service and use a reference parameter to distinguish among the active subscriptions.

from the SubscibeResponse section

1st bit of text is from top of 2.4

2nd text is from subscribeResponse