You're right, @nicgas. But, frankly, how many native English speakers know what a subjunctive is? If you had a look at other languages, you would see subjunctives are nearly dead grammar forms so this topic isn't taught even in those languages. There is no sense in explaining subjunctives to foreign students as they wouldn't understand it, no way. The fact is that we use grammar forms our students can understand and already know. There's not any difference except for a very formal form of "be" when only "were" is used. But, in any informal usage "was" is okay as well. Anyway, I am a member of a group of English teachers (mainly American and English natives) on linkedin.com and the question of the need for subjunctives in modern English was discussed there several months ago, and the result of that long discussion was that there was no reason for anymore. Each language is a "living" system, and it develops all the time being influenced by a lot of factors.
Conditional Sentence Type 1
→ It is possible and also very likely that the condition will be fulfilled.
Form: if + Simple Present, will-Future
Example: If I find her address, I’ll send her an invitation.
more on Conditional Sentences Type I ► Conditional Sentence Type 2
→ It is possible but very unlikely, that the condition will be fulfilled.
Form: if + Simple Past, Conditional I (= would + Infinitive)
Example: If I found her address, I would send her an invitation.
more on Conditional Sentences Type II ► Conditional Sentence Type 3
→ It is impossible that the condition will be fulfilled because it refers to the past.
Form: if + Past Perfect, Conditional II (= would + have + Past Participle)
Example: If I had found her address, I would have sent her an invitation.