NOC_NA just posted the information Dec 26.
There is now new group lettering for these legacy-only reductions. "Group A" is the "World group 3" of the 5 groups of the patch notes, and is the target that legacy world prices would be reduced to. "Group B" is the less expensive legacy tier (NA data center), and "Group C" is the more expensive legacy tier (JP data center).
They don't say when the first adjustment will happen. It hasn't happened yet (lowest small is still ~19M on Group B). I hope it will be in a day or so, but I expect it will happen by early January at the latest.
Price reductions for Group B (my calculations of starting prices for lowest-priced S/M/L):
Originally: 20M/75M/250M
First reduction: 18M/68M/225M
After a week: 16M/60M/200M
After six weeks: 8M/30M/100M
For Group C (my calculations of starting prices for lowest-priced S/M/L):
Originally: 40M/150M/500M
First reduction: 36M/135M/450M
After a week: 32M/120M/400M
After eight weeks: 8M/30M/100M
If January 1 is the first reduction, then Group B pricing could hit target around mid-February, and Group C by end of February.