Let’s say he was so ashamed that he couldn’t bring himself to attribute the word to his own actions. After Seccuro explicitly said she wanted him to call a spade a spade, he probably felt that he couldn’t just keep on sending messages that used roundabout terms. At the same time he (let’s say) might have felt that since the topic of his language had been breached, he felt more able to use the word (I’m not sure Seccuro’s e-mail was actually the first instance of the word “rape” in the entire conversation; if not, then this part is probably not relevant). His lawyer wants to say that rather than now feeling more able to use the word, he merely went along with her categorization of the event in deference to her being the apologizee.

Then you have to ask: first, how likely is it that he was really just being polite? and second, does it even matter if he was doing that, or can just the words “I did [rape you]” say all there is to say? I agree that the lack of hedging material (like scare quotes) is an important point against his case. So if you want to accept the argument that he was being polite, then you have to ask: did the context of the sentence preclude the use of such punctuation, even if it “should” have been there?

But, fortunately, there’s other evidence besides just the communications (like submitted eye-witness accounts and other written records from the time, not to mention what Seccuro has to say about it), so in the end it may not matter why he never used the word “rape” until he did; the mere fact that he admitted to any inappropriate sexual conduct is enough.