Only one thing can exist in one timeline, in regular circumstances, without any dimensionel\time travel. There's one pendent, it exists until 1000 A.D. If the 1000 A.D. pendent is taken back to Zeal, the Time Bastard effect does not take any effect, because the two pendents, although the same, have no effect on one another. None of the two contradicts the existence of the other. There's the future pendent, who happans to be in Zeal, and the past pendent, that also happans to be in Zeal!
Same for my Janus example. Same for the fact you can have two Zappas in Another World, two Korchas and two Machas in Home World, etc. They do not contradict each other's existence (Bad example, actually. They can't, they're no longer connected).