You can press dry-sifted hash but it usually has trash in it that prevents the heads from melting together uniformly; really depends upon how gently it is bounced. Dry-sifted kief is pretty good as it is. I just top a bowl with it. Usually made from whatever falls on/through my sifting screens when trimming and the occasional larfy loose bud. You could try to “clean” it with different size micron screens but it takes some effort.
Water (bubble) hash is filtered so if you do it right all your full melt should be in the 74u or 45u bags. Resin heads are typically around 50 to 100 microns; you need to separate them from everything else to make full melt hashish. “Full melt” meaning you have separated the resin heads and only the heads so when it is dried and pressed it is dabb-able; melts on a nail. That’s the shit, son