Good thing...
They didn't figure out their purpose until Hal showed up and told them.
Amongst all of their unfinished business, only Harrison's was plausible for Thomas to do at a young age. But, Milo returning the stamps, Penny finding out about her kids, and Julia fixing Thomas's or her own relationship is next to impossible if they attempted it in the early 60s when Thomas was merely a child.
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"Are you watching closely?" — Alfred Borden (The Prestige)