Man, this took a few tries even after I already knew what to do. The door I used to flee was a bad choice, apparently. The reason why I thought it was a good idea to use it was that in one practice run, which ended in a shootout, the guards came in through the small door, not the double doors. Use the small door that is unlocked when entering the sniping room (if you use the same one). The ending screen that says I unlocked sawn-offs is edited in, but the result screen itself is the correct one. See, the game is bugged in the way that if you reload a level you got SA ranking on and get SA again in the replay, it removes your SA rank prizes and gives you the first prize over and over again, which happened here. I foolishly thought that the game wouldn't be messed up enough to actually get rid of the sawn-offs, that the info box was just bugged and I would actually have the weapons later, but I was wrong. I don't have the sawn-offs on any file anymore. I do have the silenced ballers in the beginning of each level but the game re-awards me with them in the end everytime. I was instructed on how to avoid this specific problem even before I started recording the walkthrough, but unfortunately the instructions were completely wrong apparently, so I'll try to do the opposite of what I was told and see if that works better.