the weapon daves using in that flash is one of those weird perks of being a knight of time: it can cycle through its own timeline, back to when it was whole or forward to when its rusted. so, like when john puts the head back on a hammer to fix his specibus, Dave can access a full sword temporarily by "fixing" the sword.
So, every time that Dave does that, he’s creating an alternate timeline when his past self gets the sword taken by his future self? Though, to be fair, he could also be doing something like what was done in the Star Trek: Voyager episode, “Relativity,” where Seven kept getting taken out of her timeline, but by only fractions of a second backwards in time each time it was done. In theory, if you have the ability to do that--and who’s to say Dave doesn’t--then you could have access to an infinite number of swords.
Although... maybe Dave’s just borrowing them from a different time, and replacing them when he’s done? That way the timeline is preserved because it would only be missing for a nanosecond, too small of a time to be observed by a regular human, and Dave has sort of a dimensional anchor to a fixed point in time where he can borrow the sword.
I think about things like this way too much.
