With each character being an immortal (see Souls) that can be reborn (see Death & Retirement), the flow of time becomes an important matter.
Campaigns that span multiple lifetimes of characters do not necessarily occur in chronological order. Similar to Doctor Who, the characters may well move back and forth, timelines max loop over each other and even cover the same time again (though in a different place).
It is strongly recommended that the characters never meet themselves from a past or future time. Running such an adventure would be close to impossible and is likely to end in disappointment.