From The Stargate Omnipedia
Planet never visited by SG-1 in its first eight and a half years of operation. An SG-1 team in another quantum reality visited 455, using the planet as their starting point to pass through Kallana's black hole and enter into a reality where Earth's Zero Point Module was still charged.
Note: This planet's designation is first given as "PX7-445." All subsequent references are to PX7-455.
HOME TO - People of PX7-455
FIRST APPEARED - N/A
Ripple Effect - Stargate Command makes contact with PX7-455, where the people assure them they have never laid eyes on SG-1.