[Avodah] How does Prozbul work?

[Lisa Liel via Avodah]

On 9/16/2015 8:40 PM, Micha Berger wrote:
> On Wed, Sep 16, 2015 at 07:36:20PM +0300, Lisa Liel wrote:
> : On 9/16/2015 1:09 PM, Micha Berger via Avodah wrote:
> :> The gemara assumes that yovel de'oraisa ended when the 2-1/2 shevatim were
> :> exiled from their land be'ever hanahar. Which is a bit of a question on
> :> Rashi. The loss of the lands there did not mean the exile of the majority
> :> of Benei Yisrael.
>
> : How do you know?
>
> (I assume you mean the reisha about yovel and therefore shemittah de'oraisa
> ending when eiver hayardein was conquered, not my last sentence.)

Actually, I meant your last sentence.  How do you know that the area of 
the 2.5 shvatim didn't include a majority of Bnei Yisrael?

Lisa