I think there's a difference between "justified" and "therapeutic".

In the situation you outline, the T is failing to be responsible, because he is changing boundaries without saying anything about it. In the absence of an explanation, I think this is potentially confusing for a client, especially if the boundary returns.

I feel like if we all based our behavior on what's "justified", though, we'd all be in trouble. I have trouble relating to wanting to cross boundaries, because I pretty much don't. I did, however, have a close friendship with someone who would do just exactly this... she would occasionally poke at boundaries, looking for an opening to do what she wanted to do. And if it was ever the case that I or our other friends didn't push back, she'd go straight through with the "but you didn't say no last time" thing. For a while, we shared a workspace, and bit by bit, she would leave it messier and messier, to the point where she wasn't even bothering to put trash in the trash can, I kid you not. She was going through some personal stress at the time, so I let it go a couple times. But when that stressful period was over and she kept doing it, I finally confronted her and she blamed me for not telling her earlier not to leave trash everywhere. This is a really basic and straightforward example, but it was true with so many things that one by one, she lost all of her closest friends, only able to maintain friendships with those that were far away.

Now, it's true that I didn't tell her not to leave trash everywhere. But it's also true that she knew better than to leave trash everywhere. So was she justified? I don't know. But I do know that she'd have been better off just trying to be a good friend and maybe getting some practice in adult behavior (she was always really really messy). So focusing on whether or not she had successfully found some kind of friendship loophole really didn't help her get any closer to interacting with people in a healthy manner. She just got whatever temporary gratification she got by leaving trash on the floor. Maybe that's worth it to her, but it wouldn't be to me.

It's true that boundaries are a big topic in therapy -- some people push them, some people won't even come near them. However, it's THERAPY, not a free-for-all. What disturbs me about your scenario is not just that the T doesn't say anything... but that the client doesn't either. My T has sometimes changed boundaries without saying anything, but I usually ask him about it. Nowhere here does the client first say, "Hey, so I appreciate your letting me e-mail more than once a week last week. Is that ok for me to do in emergencies?" Instead, quite purposefully, the client pushes on it to see how long it will hold, rather than discussing how helpful e-mailing that extra time was, and whether it would be worth considering multiple e-mails per week. To me, there is a vast difference between crossing a boundary in a tough situation and then revisiting it, and crossing a boundary in a tough situation and then continuing to cross it as long as nobody says "no", and purposely not asking about it in order to milk that implicit "approval" for all it's worth.

I lay a lot of responsibility at the T's feet to keep everything on a therapeutic track. However, if a client is doing the "not no means yes" thing in order to cross what used to be an explicit boundary... whether it's justified or not, they must be aware that they are pushing their luck, otherwise they would just ask about the boundary (or not push at all, of course). Only a superficial level of self-examination is required to see that this is probably not a productive behavior.