Tense simplification in subordinate clauses -the very difficult subject

1) "It would have been kind to give the source, so that this was clear to people."
1-1) "It would have been kind to give the source, so that this would be clear to people."
2) This discovery will mean that we spend less on food.
2-1) This discovery will mean that we will spend less on food.
3) At the end of the year there will be an exam on everything you've studied.
3-1) At the end of the year there will be an exam on everything you will have studied.
4) In a perfect world, you would be able to say exactly what you thought.
4-1) In a perfect world, you would be able to say exactly what you would think.

a) Can I use all the examples above?
b) I'd like to know what case the tense simplification is imperative in? - for example, only when I use adverbial subordinate clauses of time and condition, is the tense simplification imperative?

Thank you in advance for your help.