Student or Learner
"In the last 10 months, the following events were important for our company."
Would "have been" be correct? "Were" should be correct because we are talking about a specific period of time.
The present perfect is more natural to me, a speaker of BrE, but the past simple does not sound strange.
I think you may be partly right with your suggestion about were. The speaker is considering the last ten months as a completed (rather than specified) period of time.