You need to go rewatch the scene again, because at no point is the torture ever shown to be successful or help in any way at all, whatsoever. In fact, at no point does he ever say that he can't remember anything else; Mr. K says repeatedly that he has more information but both Mr. S and Mr. T ignore him as neither are prepared to listen. In fact, the Interrogator, instead of actually trying to find information, spends most of his time taunting, belittling, and threatening Mr. K rather than asking him for information, or distracting him with torture or threats to prevent him from actually thinking of anything. Allow me to give you a play-by-play:Lykosia said:Mr K. says several times that he doesn't know anything more and he is telling everything he knows, but then he knows and remembers more things after the torture, which is pretty clear to me that the torture was working.
0:00 - Initially, Mr. K has literally no idea who the fuck they're talking about. He has already given them a random address of a former Azerbaijani client of his hoping it's the right one, but it isn't.
0:30 - He still doesn't know who they're asking for. Rather than give any names or details to help narrow down the search, T just starts torturing him because somehow they expect him to know anything.
2:00 - They finally tell Mr. K the name of the man they are looking for, Tahir Javan. Mr. K shouts: "Why didn't you ask me!?" and reveals the address.
3:00 - Mr. T gets the instruction to "loosen him up" because they need a description of the target, but they don't ask any questions. Mr. K shouts: "I'll tell you whatever you want, just tell me what you want!" but to no avail: T gets right to work with the next torture instrument. By now, a pattern emerges: he keeps getting distracted by the threats of torture whilst the Interrogator and Torturer completely ignore any answers he gives.
4:35 - Finally Mr. S poses the actual question: what does he look like? His mind rattled with the recent torture, he tosses out the first things to come to mind: "average height, weight, and build, dark hair"... before he's given a chance to think of anything else, the interrogator walks away. Relieved, he takes a few short seconds to rest, and think of more details.
5:41 - He's not allowed to give a better description before the torture begins again; by now, he understands the pattern: regardless of whether he has an answer or not, they aren't prepared to listen to him, they're just going to torture him.
6:23 - He finally gets the opportunity to give the torturer the answer he's been trying to give them for the past minute and a half: he's got a large beard. Apparently that's good enough because Mr. S just gets back up and walks away instead of waiting just a little bit to see if there is any more information. The interrogator starts taunting Mr. K, implying that he's going to have him killed if they don't get better information; with such an imminent threat to his life hanging in the air, Mr. K is YET AGAIN distracted from the ACTUAL TASK AT HAND of giving a better description and, with the spectre of death looming over his head, he shouts: "No, no, no, no!"
7:30 - They keep demanding more information, but right now he can hardly think. Worse, he knows they're going to torture him right away regardless of his answer. And guess what: even though he gives them loads more information now that he's been given a half minute to think, they still torture him again for no fucking reason at all.
9:00 - He just repeats what he's already said before the latest torture, insisting that he doesn't know any more. And guess what: it's good enough.
Literally all of his answers come from when he's had a break from torture, but they always go straight back to torturing him and ignoring any answers he tries to give them.
Quite literally, the entire process could have been skipped if they had just figured out who he was and then asked him about his former clients. Instead of nine minutes of torture to get a simple description of dark hair, beard, smoker, and left handed, they could have done it in 3 or 4 with no torture.