I see, wow, it never occurred to me so. What that implies seems to be: if a fund/stock that had been purchased at various prices was later sold with huge gains in one transaction, and the sale price is higher than all but one purchase price, then the loss from that one particular purchase can not be claimed if new purchase is made within 30 days of the sale. ?
If so, it seems it would be prudent to ALWAYS wait for 30 days before buying back, unless it’s clear all the purchase prices were lower than the sale price.
(In all the years I filed taxes without being aware of this, and it never occurred to me as an issue. But I think I may have never bought back a fund/stock within 30 days of sale anyway.)