I don't think its always productive nor meaningful to attempt to link authenticity to a reference in the Tipitaka. The Theravada is a living tradition and has evolved over time. It is also a living tradition in the sense that the Dhamma, if it is to be meaningful, must be integrated into one's life to the point where its a lived experience.
Personally, I tend to think that there is a place for relics and relic veneration in the Theravada. Relics are merely an object that inspires saddha. And without saddha there can be no panna.
“No lists of things to be done. The day providential to itself. The hour. There is no later. This is later. All things of grace and beauty such that one holds them to one's heart have a common provenance in pain. Their birth in grief and ashes.”
- Cormac McCarthy, The Road
Learn this from the waters:
in mountain clefts and chasms,
loud gush the streamlets,
but great rivers flow silently.
- Sutta Nipata 3.725
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