The bare verb in Chinese can communicate many different things, depending on context:
A habitual action: 在他家发生的事情，我没法了解 = I cannot understand the things that happen at his house.
An ongoing action: 正在发生的事情挺可怕 = The things happening right now are very scary
Future action: 未来发生的事情我没法知道 = I have no way of knowing what will happen in the future
Past action: 昨天发生的事情很可怜 = What happened yesterday is a shame.
What difference would there be in these sentences if the traditional "tense" words are added, whether they be auxiliary verbs (要，会）, or verb suffixes (了，过）:
未来会发生的事情我没法知道 = ？？？ 昨天发生了／过的事情很可怜 = ？？？