Stalker,
Undefined,
17 years ago
There are many different possibilities, the main one being, as you suggested, the need to actually earn the acid proof weapons. Although part of the challenge of the blooding hunt would be to make things as difficult as possible to truly test the unbloods, so they may have purposely had their standard wristblades (& possibly other weapons) taken from them, & been fitted with a new set specifically for the hunt, which would be susceptible to the acid. This is highly likely, as it was shown that they "loaded" a new pair of wristblades into their gauntlets as they prepared themselves inside their ship.