What am I missing here? If my evaluation is correct, it seems like the critical difference is primarily in whether the individual is trustworthy, not in what the person's claimed status is.
You aren't missing anything but my way of thinking on this goes as follows.
1) Guys who are not on PrEP.
A tiny number of infected people will still test negative at three months, as they are slow to sero convert, so this isn't completely reliable but, on the whole, it's good enough. If you receive a needle prick injury when working with blood that potentially has HIV (this happened to my mother) testing at 6 months is required to completely rule out HIV infection.
Lots of guys who aren't on PrEP don't understand the whole window period malarkey. If you're finding a random person to have sex with, on somewhere like Grindr, then they are most likely engaging in regular casual sex. This isn't always the case, but on the whole, I wouldn't trust someone to remember the exact date they last had a shag unless they had texts, or similar, in their phone, to remind them. Some won't have had sex for a long period of time, because they don't have casual sex, so with them there's nothing to remember. It could have been well over a year and they've been tested within the last month or so. These people should be guaranteed to be negative but, unless you're in a relationship with them, you aren't going to have sex with them.
2) Guys who are on PrEP.
This should theoretically be incredibly safe but it has been shown that being forgetful is a thing. If you're taking it one pill a day, and have been taking it for months, then missing one day, every once in a while, isn't going to do much. It has been shown that taking 4 pills a week, they call it the Ts and Ss, (you take pills on Tuesday, Thursday, Saturday and Sunday) also provides an excellent level of protection. So if you accidentally go down to 6 pills a week, when you forget a dose, it's not really that much of a problem.
The guys taking PrEP know that they need to do this so they don't get HIV. Thus the incentive to remember to take it is high. Nevertheless this is a risk you take when trusting someone. If you are talking to someone about barebacking with them and they mentioned they are on PrEP, either in their profile, or during the conversation, then it's wise to ask them questions about it. Say things like you're interested in taking it yourself and get them to talk about it with you, discussing side effects they had, how long they had to wait until they were told it was safe to go bareback, where did they get the pills, how can you go about it etc. Know this information yourself before you talk to them. If they don't know a lot about it, take forever to answer, as if they are looking the information up, or seem stingy with the conversation, don't meet with them.
3) Guys who are HIV+ but UD.
There's stigma attached to this. A whole lot of stigma. No one is going to advertise themselves as HIV+, undetectable or not, if they really are HIV negative (or believe that they are). If someone wanted to trick you into barebacking with them then they'd try pulling fast one by lying about being on PrEP or lying about their recent HIV tests/recent partners. In the first case they'd scare away lots of men who don't understand UD means untransmittable and make the job of hooking up even harder.
No one with HIV wants to give HIV to anyone else unless they are insane. It's also illegal to lie about your status in a situation where you know you're HIV+ and are going to engage in any activity that could infect someone. People who take PrEP know that taking it stops them from catching HIV, it's a good incentive to take it. But those with HIV know that taking their pill(s) stops them from
dying. An even
bigger incentive to take them if you ask me! So they are unlikely to forget, or will have timers/reminders set up so that they really don't forget. There is the slim chance that an UD person might not be UD due to forgetting meds or their status having changed since their last check-up, but this is unlikely.
Besides their status, what else could a positive person be lying about? If you're going to have sex with them the only thing you really care about is if they are in fact UD or not. And, as I said before, lying about that is illegal. It's also fairly simple to ask a HIV+ person when their last check-up was and what medication they are on. Ask questions about it to see if they have the right answers. Most HIV+ UD people are perfectly aware that there's stigma and are perfectly happy to discuss things, if it helps put your mind at ease, before fucking with them. Just be polite and friendly. If you are polite, and friendly, and are met with incorrect answers, question dodging, delayed responses, or just the person turning hostile, block/forget about them. This isn't someone you want to be meeting with. Heck this isn't someone you want to be meeting with for any reason lol, let alone sex.
Though my absolute number one piece of advise is to ask if said person is drunk or high. First of all their dick probably won't work well in either state and no one wants to play with that. Secondly substances affect the brain and you don't want someone, with an impaired state of consciousness, answering your questions about their sex life.
No one is perfect, we all forget to ask certain questions before meeting up with someone some of the time, god knows I have, but just be careful and if anything feels weird don't go.
Lots of them have wives.
