I *think* the "subsequent beneficiary" is still grandfathered under the pre-SECURE Act rules (because the original beneficiary died in 2012--if the original beneficiary died instead in 2020, we'd have different rules to follow).

Under the pre-SECURE Act rules, the subsequent beneficiary essentially steps into the shoes of the deceased original beneficiary and continues subtracting 1 from the original beneficiary's life expectancy when the account was inherited.  So if the original factor was 43.6 years, the original beneficiary would take 1/43.6 of the account in the first year, then 1/42.6 in the second year, then 1/41.6 in the third year, and so on.  The subsequent beneficiary continues with 40.6, 39.6, 38.6, etc. (wiggle the numbers as needed to fit your set of facts.)

If we walk back in time we can find a Pub 590 from 2012:

https://www.irs.gov/pub/irs-prior/p590--2012.pdf

Jump to page 37 and find this in column 2:

Other designated beneficiary. Use the life expectancy listed in the table next to the beneficiary's age as of his or her birthday in the year following the year of the owner's death. Reduce the life expectancy by one for each year since the year following the owner's death. If the designated beneficiary dies after  September 30 of the year following the year of the owner's death, continue to use the designated beneficiary's remaining life expectancy to determine the distribution period; do not use the life expectancy of any subsequent beneficiary.

Rick