The SMDR has a buffer. Once you place a device to capture the data, the buffer will output everything in it. Usually, the system is set up to have the buffer be overwritten when it gets full. The oldest calls will be discarded for the new calls. Hopefully, you have not reached that point.
If the SMDR data has already been outputted and your device was receiving but not capturing the data properly, I am fairly confident that those records are now gone. Once the data has been sent, that's it.