Multiple registration using single UA

If I wanted to register two distinct numbers through a single UA Device
say 34111111 and 34111112 through one/single UA Device.
Should I expect the "Call-ID" to be Unique or  Identical?
RFC3261 seem to imply that the only the "SIP Tag"  needs to be unique for
the SIP Server or Registrar to
understand that both Numbers are being registered from one device only.  How
could the SIP Server or
Registrar verify that these two numbers are in fact originating from the
same Device?
Thanks in advance

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