Three runes: past, present, future
Three runes are drawn, and each answers its own position. The count is as old as the oldest description. The positions are not: past, present and future is the shape of a card spread, and no runic source carries it.
Where this comes from
oldest description Tacitus, Germania, chapter 10 · about AD 98
Tacitus has the priest lift three of the scattered lots, one at a time, and gives them no positions. Nothing in his description says the first is the past or the third the future. The number is ancient, the meaning of the positions is not: no runic source assigns positions at all.
What the poems say
None of the four witnesses describes a way to cast or read the runes. The poems describe the letters, one by one, and stop there. What each rune means in them is gathered here, rune by rune.