I must be missing something, Freddy (maybe I have a screw loose?). You said: (a) ' My repair regime has 9mm ply glued to the loft side of the plasterboard, and screwed down from the bathroom.' and (b) 'If read 'as written', the subject was the ply, which I assure you was screwed down to the plasterboard.'
If you are truly saying that you screwed through the ply into the plasterboard (really - and got a decent fixing?), then I accept your screws were and remain pointing downwards. But, if the loft was above the bathroom (as in most houses!*), how were you screwing 'down from the bathroom' rather than 'down from the loft'? I think we should be told.
* Except presumably that built for the kinky architect who had his house made [ or was it 'housemaid'?] upside-down.
In suggesting that your repairs might outlive you, I intended no compliment - just likely fact!
I sympathise about you tool-related technophobia, having had treatment for this myself (no ointment involved). Until about five years ago, when the mammoth flat rebuild started, I owned no cordless tools (bar a pathetic cheapo screwdriver) and could see little merit in them. But, having used a friend's cordless drill on a project we were sharing, I realised its convenience, at least. Now, two cordless drills later (one being used almost entirely for screwdriving), I admit their merits in awkward places - but prefer mains power when practicable and have no intentions to expand the portfolio with jigsaws, circular saws, routers, planes etc. (My words may yet come back to haunt me.) And the auto-feed screwdriver isn't cordless either, although it would have been quite handy if it was. It cost me about £22 on eBay and earned its keep very rapidly with close to 5,000 screws to insert - although a fair number needed that final twist with a manual driver when the studs (e.g. oak) were hard.