Hmmm, let me check... OK, here's the
link.
It just says there >were< 3 of them in existence, with no source for that statement. Episode indicated just shows the capacity to stun / stasis someone.
Of course, in B5 lore "were / are" are a subjective term, keep in mind how Zathras spoke of The One (One that was, One that is, One that will be).
Also, B5 Wiki, War Without End, pt.2, act 5 description:
"The
White Star emerges from the time rift back in 2260. As they exit, the time rift closes and all temporal distortions in
Sector 14 cease: its role finished at last. Delenn reveals that this is not the only circle that is closing. She reminds him of the fact that Human and Minbari souls began crossing one thousand years ago. Her transformation into a part-human hybrid was part of an effort to correct this imbalance,
but now she reveals an insight into what started it. The Triluminary that brought about her transformation also came from one thousand years ago. Someone had to present the station to the Minbari in the past, and they wouldn't have trusted a human. A stunned Cole realizes the implication: "a Minbari not born of Minbari."
So it could well be just that, the three Triluminaries are in fact: the Triluminary that was (brought by Sinclair -> Valen), one that is (same item, used by Delenn to turn human-like), and will be (used by Sinclair in future / past as the loop is completed once more).
Also, this brings up an interesting point, since the Triluminary used by Grey Council to "test" Sinclair and indicate him to "have the soul of Valen" is literally the same one that Sinclair used to "Valen-ise" himself in previous time-loop, it could well be argued that it's not so much the Triluminary did truly scan and confirm Valen's soul, but simply detect Sinclair's DNA* and go "Oh, it's
you again. Like...didn't we do this before? Or do you want another round of the same?"
With Triluminary being "our most holy relic", it's extremely unlikely the Minbari would ever disasseble and analyze it so see
what is it exactly,
what does it do and
how does it do what it does. Much rather they'd put it on a shelf somewhere and
venerate it. Thus mistaking a genetic (re)sequencer** for a soul detector.
(*) (**) Because DNA scanning and resequencing is exactly what it does, it turns a Human into Human-Minbari hybrid, then a Minbari into Minbari-Human hybrid. Over and over again. So nothing to do with soul engineering, just plain old genetic one...
In short, Minbari surrendered in BotL for wrong reasons...