Doubt about third conditional sentence

Question

This is a sentence from Death Note. The assassin has just said "I am victorious!" thinking his plan to kill everyone was successful. But being alive and still, the detective says:

あなたはさっき、自分の勝ちを宣言しましたが、確かに本来あなたは勝っていた。私は負けていました。

At first, I read this last part as "Originally you were winning and I was losing". But I decided to check the official translation both in English and Portuguese, and they both translate as "As a matter of fact, you would have won and I would have lost" with the "if things had gone your way" implied.

So, both English and Portuguese translate it as the second part of a conditional sentence, a third conditional sentence where the IF part is implied.

I don't actually know how to produce this grammar. Or even recognize it without the help of context. Since all I see is the use of past continuous tense.

If I want to make my own sentences, let's say: If I had studied more, I would have passed my university entrance exams... What kind of grammar would I have to use?

I have seen other posts working on that subject and explanations that past tense in Japanese can be subjunctive, and actually mean hypothesis and so, and it just got me more confused.

Answer 1

I don't think past continuous tense has any function to make sentences hypothetical.

確かに本来あなたは勝っていた。私は負けていました。

This sentence states a different possibility from the present situation and it's the work of 本来, not past continuous tense. Simply speaking, it can be translated as:

Originally, you should have won and I should have lost.

On second thought, we usually put the opposite sentences right after the word "originally", right?

i.e.) I would have studied abroad originally (if nothing had happened), but I decided to stay in Japan because of COVID

So, I think the word itself has a hypothetical nuance, which addresses an event that might have happened if nothing had happened. This can be the reason why they translated it in hypothesis.

On the contrary, I can see a clear hypothetical precondition in the following sentence:

If I had studied more, I would have passed my university entrance exams

So I'd simply say 「もしもっと勉強していたら、大学に入学できていただろうに」or something.

Answer 2

本来 is not infrequently followed by なら・ならば, and had that been the case here the conditional would have been more obvious. It is fine as it stands however, as the previous answer points out.