My theory is that we don’t have enough information in the pic to assess the accuracy of the claimed dates.
To your counter, why did Reagan raise taxes? What happened before, what happened after? Did it disproportionately favor the wealthy? Is it inaccurate to include his rise to power if it ultimately led to the policies we’re discussing? When do you think we should begin counting? When he first took the Presidency? When the first trickle-down policies where proposed? When they were enacted?