"The 8915B for 2018 shows the 30K and the 10K taxable"

That would make it a 2017 Disaster, then. B = 2017.

"Use 2019 Form 8915-B if you were adversely affected by a 2017 disaster listed in What 2017 Disasters Are Covered, later, and you received a distribution that qualifies for favorable tax treatment. For distributions for qualified 2016 disasters, see Form 8915-A and its instructions."

"File 2019 Form 8915-B if either of the following applies.
• You received a qualified 2017 disaster distribution in 2017 or 2018 that you are including in income in equal amounts over 3 years.
• You made a repayment of a qualified 2017 disaster distribution in 2019."

That form suffix (the A or B or C or now we expect an E; whatever) is driven by the Year of the Disaster, not the tax year. The Disaster is declared and the qualifying dates and the dates of distribution that apply (for instance, whether or not it is allowed to have a distribution for a Disaster event in one year that will overlap year end) and repayment timeliness is listed in the instructions for the form. The distribution is for that disaster, but it could be a distribution for the same year as the disaster or the year after it and it has to meet the instruction requirements, of course, and it would be for purposes of recovery and repair. You didn't note which disaster it was for or compared to the Date for that Disaster. Go here:

https://apps.irs.gov/app/picklist/list/priorFormPublication.html?value=8915&criteria=formNumber&subm...

To see how there is a -B revision for each tax year that would apply (2017, 2018, 2019) for the three-years of allowed deferral/repayment window for 2017 Disasters.

You can get the IRS transcript for 1099-R for 2018, to see how the brokerage reported it.