～たまで + だJust, Merely, Simply, Only

These are essentially the same grammar pattern, with the difference in nuance coming from the verb tense. ～たまでだ is typically used to downplay a completed action, e.g. 自分の意見を述べたまでだ ('All I did was express my opinion.), while ～るまでだ generally implies the speaker will 'just do (something)' in the face of a bad situation, e.g. 誰も教えてくれないなら、自分で調べるまでだ ('If no one will teach me, I'll just look it up myself'). Both are typically used to refer to one's own actions or those of someone in one's in-group.

Both それまでだ and たまでだ use までだ to mark a limit, but the type of limit is different. それまでだ expresses a harsh evaluation meaning “that’s all there is” or “that’s the end,” often used to judge that nothing more can be done if a condition is lost, as in 信頼を失ったらそれまでだ (‘If you lose trust, that’s the end.’). By contrast, たまでだ uses the past tense to downplay an action and means “I only did (A),” emphasizing that the action was small or not worth blaming, as in 俺はただ自分の意見を言ったまでだ (‘I only expressed my opinion.’) or 困っていたから助けたまでだ (‘I just helped because she looked troubled.’).