We also use the Present Perfect to talk about several different actions which have occurred in the past at different times. Present Perfect suggests the process is not complete and more actions are possible.
Last year means the year before now, and it is considered a specific time which requires simple past. In the last year means from 365 days ago until now. It is not considered a specific time, so it requires Present Perfect.
We use the present perfect to talk about
I've cleaned my shoes. (So they're clean now.) Mr Green has bought a new car. (So it's his car now.) Joanna hasn't eaten any toast. (The toast is still on the table.) Have you finished the housework? No, I haven't. I'm still doing it.