In a word- Oh yeah.
A “bulletproof” vest works by being woven of very, very strong thread- variants of Kevlar, carbon fibers and “Beta” cloth, among others.
What this does is… well, the fibers don’t break when struck by the bullet. This forces the projectile to deform, which spreads it’s impact area out over a larger surface. The threads also tend to keep the projectile from penetrating.
However, a crossbow bolt typically has a nondeforming steel point, which can easily defeat a vest. A hunting type broadhead with two to four razor-sharp blades would have even less trouble.
Same goes for a knife- the edge can cut the fibers, and the point does not deform. It may well be more difficult to pierce a 'vest with a knife than a normal coat or jacket, but it’s still possible.
As for a 12-guage slug, or other, “heavier” calibers, vests are rated for certain “threat levels”. Meaning a certain vest is usually resistant up to and including, say, .357 Mag shooting a 125 grain bullet at up to about 1,200 fps.
A heavier bullet, or a lighter bullet traveling faster, or the same bullet in a nondeforming style (such as military “ball” ammo) have a better chance of defeating the armor.
In the case of the 12-guage slug, even if the vest were rated near that energy level, and perhaps had the optional “trauma plates” (typically, add-on sheets of titanium or even fiber-reinforced ceramics that can augment the threat level of the vest, or provide additional penetration protection) the sheer energy of the slug would cause major concussive internal injuries.