I recall that waay back in second edition magic items bonus was reduced the farther the item got from the plane it was created on. I just don't recall how that worked. Please enlighten me.
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Outer Planes <-> Astral <-> Prime <-> Ethereal <-> Inner Planes
For every step on the list above that an item moves away from the plane of its creation, the bonus drops by 1, to a minimum of +0 (still magical, but no bonus).
If an item was forged in a particular Outer Plane, its bonus drops by one on adjacent Outer Planes, and by 2 (as if the trip were counted Outer -> Astral -> Outer) in any other Outer Plane. Items forged in Sigil or the Outlands are fortunate in that respect. Likewise the Inners. The largest possible drop is -4, for an item taken from an Inner to an Outer Plane or vice versa.