If it wasn't leaking or noisey when you took it off, then I would say It's OK. But if it shows signs that it was dripping (you can tell by the little hole under the housing directly under the impeller drive shaft) You may see a little water/antifreeze stain there. If you are doing a new engine and your pump is any more than a year old, I would have it rebuilt or replaced. If It's easily accesible and not too much work to remove you might want to use it, but pumps aren't that expensive. (Don't know about the Netherlands) I would replace it if It's not nearly new.
But you never know! The old one might last longer than a new one! One of lifes many misteries.
Since it's off, can you put it in a vise or something to hold it? The, with the fan blade one, see if there is any side-to-side play which will indicate bearing wear => replace it.
69 RS Conv therapy program, Autogear M22, 8-pt cage, with a new 410! SOLD
New therapy program - 68 Coupe. Will be survivor exterior, modern underpinnings! SOLD
67 Belair with perfect floors, pinchwelds and firewall. Hmmm!