Simple Q&A D&D 3.5 (by RAW) XXIII

[Curmudgeon]

A 102

Once your demiplane is created, you can travel to it using astral caravan, plane shift, or some other power or permanent link that you arrange for separately.

Because the power says you can travel to the demiplane using one of these effects, you can.

A 103 No.

It doesn't mean that you can arrive perfectly at your destination if starting from somewhere other than the Material Plane; it just means that if you start elsewhere there is no specification of how far off you arrive. You'll have to ask your own DM how far off they want you to to arrive for other planar starting points. Personally, I use the same off-target formula for all planes, as that makes my job as DM easier.