IRCC is asking access only for last three years income proof immediately on the date you submitted the application, not on date of submitting interest form. So there is not a question now for 2018 or 2017 income requirement, that would be an issue if someone got invitation last year or previous year.
These are some contents copied from CIC website:
If you’re invited to apply, you have to
provide proof that you meet the income requirements for each of the 3 tax years before the date you apply.
We can’t assess whether you meet the income requirements until you apply (if you’re invited).
Note: For the 2022 process, we’ll assess sponsors on their income for tax years 2021, 2020 and 2019.