oddly enough getting better with age seems sort of common with these machines ... I had a 7900 that exhibited that, and my 9900 rarely shows missing nozzles any longer, when new I had a few show up once a week or so. I've had others who have purchased them report similar experiences, although there are certainly many that never mention any issues with missing nozzles.
These printers do like to be used ... the more they run the better they seem to perform.