Commitments attach to diegetic disclosures such that
asserting X sans caveats justifies
reliance on X.
GM: "Tommy tells you they straight-up saw the Supervillain put the Will into the safe before they left for Frankfurt last night."
The right person said the right thing at the right time, so it's added to fiction without further negotiation. By contrast
GM: "Tommy kind of squirms and tells you they saw the Supervillain put the Will into the safe... just before they left for Frankfurt. Umm, that's right... must have been last night. Yeah, last night. For sure."
It is (in whatever way is effective at your table) squarely signalled that Tommy's testimony is unreliable, an effective caveat. This could be reasonable where locating the Will was going to be interesting. Such as - the Supervillains MO is traps and ambushes, set up by dupes. Are you
really going to walk into one for the Nth time?
Absence of caveats up front doesn't necessarily prevent twists between now and cracking the safe, but such twists will themselves be disclosed. Not hidden. So the way in which it is "binding" is,
provided nothing changes it between now and such time as player puts it at stake. Given nothing changed it, it's still reliable. And hidden changes are not permitted. (Intuitively, exceptions are always going to be possible, given the boundless scope and versality of imagination. Maybe a special circumstance comes up where it works out for information to be hidden?! If it did, we could probably analyse it to derive a principle.)