BioAmber Inc fka BIOAQ

[trader59]

The brokers only have 1 way to show the loss in the current tax year, and that's to show a "sale" of the stock for essentially nothing (think some of them would show $1 for the lot). That would result in the holder "losing" the worthless stock.
The tax loss can be claimed without forfeiture of the worthless stock for the year in which it became worthless (2019). You have 3 years to file an amendment (April of next year) and show the loss. The broker doesn't even have to be involved, file the form, provide supporting information (FINRA action suspending the CUSIP and deleting the ticker for bankruptcy liquidation, Delaware voiding the corporate charter, there's loads of options here), calculate the loss, apply it to any gains for that same tax year.