Most contracts that dj's use here do say that a postponement within a year of the original date is the only way to hold on to a retainer and not require additional payment. By the way as of today I've spoken to 4 venues as well, and all have said the same thing. Their lawyers have said they're protected as long as they don't initiate the cancellation, as they don't have a provision that covers pandemic.I also think it's going to be the LEGAL thing to do in many/most instances since WE can't perform on the agreed upon date along with the client.
There may be some leeway if your contract specifically addresses situations where BOTH parties are affected and the language stipulates that a postponement is the recourse. I would take the bet that most small claims courts will rule in favor of the client on this one.