Yes, absolutely!

If your life got busy at the time that you requested an address to send a postcard and were unable to do so, you can still send the postcard late. Just make sure that you send the postcard within a year of the date you requested the address. Also make sure that the member whose address you were given is still an active member of Postcrossing. Once the member gets the postcard and registers it, the postcard will be registered as a normal postcard.