edd,
unfortunately I would really just be guessing.
But the “Evidence of job stability” does say quite a bit and the fact that you say that they have advertised the job before (more than once) does suggest that they have had people come (take time to get up to speed, learn the job) and go (elsewhere for more money, dont like the place who knows?).
Persistance can pay off.
The interview does rely on you being able to convince them that not only are you the one for the job (that you can do it) but that (if you do not already live locally that you will move) you will STAY a few years.
Other than that I can only really guess.
Sometimes (CVs do not get beyond the personnel department) so a phonecall to the Production Manager / Design Manager can lead to something, or send application / CV direct to Prod / Design Manager (get their names and spell them correctly etc).
Other than that its have a look at some interview technique type books: Patrick Quinn , When Do I Start? is a bit dated but gives you some things to consider.