Discount rate index

How the Discount rate setup is working when creating a lease.

We have the ability to add multiple discount rates in the setup with only an Effective Date distinguishing the rates. I want us to understand how the setup will impact leases.

1. When we add a new rate with an effective date, does that mean the old rate is essentially no longer active?
2. Does a change in rates impact existing leases that have this rate applied or does the original rate stay and continue to be used by the lease even after new rates with effective dates are added?
3. Does the effective date align with the lease create date or does the module use lease commencement date to determine which rate it picks?