The reason the long since deceased 727s populate is because there are no photos of the new A320s ecetera in Airliners.net.
I have to be fair to Airnav and say that they have provided the system that gets it right 99% of the time because there is currently no system available from anyone that allows for 100% accuracy, because no-one can has a system to discriminate photos for miscodes where two aircraft use exactly the same code, that is for the air traffic authorities to request that the offending airliner fixes the problem. All any mode_s logger like airnav can do is note the anomaly. When two aircraft have used the same registration but there are no photos on the web of the newly registered aircraft there is also not much that can be done by anyone except to accept the old picture and manually update the surrounding info. You cannot have a system that blocks the photo download until you know that a photo of the new aircraft exists!!
For the known fleets of registration reuse, Qantas A333, German A319 & A320, just accept the 727/B741 picture, manually copy over the correct details from airframes, this will ensure that the correct details then go into mylog. Then a month or so after new aircraft delivery, check back to Airliners.net to see if a picture of the new airframe has been uploaded. Once a photo is there simply delete the photo of the retired airframe from the photo folder in windows explorer explorer, delete the details from one field in mylog, then do a mylog populate to trigger a search for a new photo which will be of the new airframe with the correct details.