OK - very interesting.
The iExplorer software works very well, for which many thanks.
However, despite having been incorporated as clips in iMovie, the original mp3 files, the ones I wanted and were AirDropped to me, aren't there.
At the time, the AirDrop only offered iMovie as an option, not iTunes, or anything more appropriate. I was away from any internet (in India). So the mp3s exist only as part of an iMovie project (for each one), which is absurd.
The clip cannot be extracted from iMovie on the iPad. I have tried transferring a whole iMovie project to iMovie on the Macbook Air, but it can't do it - "failed to import the iOS project file". It may be that a fully paid for iMovie app (as opposed to the one that came with the Mac) can extract the mp3s, but I'd rather not give Apple the money for something that should be doable natively.
So I am exporting an entire no-pictures movie (two hour's worth each) to the Macbook, for each mp3, which takes AN AGE, at which point it will allow me to make an m4a version (tried it with something shorter) and that'll be my way in.
Its all very well to talk about "app centric", but we are still dealing with files, and in the case of AirDrop, very much dealing with files. I wanted the files on my ipad until I got back to the UK and could do something with them. But it seems Apple won't let me do something this simple. Or am I missing something?