Okay so after doing no climbing or training all summer, I tried an opposite hand towel-assisted lock-off today and was surprised to see that it was exactly as easy as when I last tried it. I ended up holding my chin well above the bar and the lower arm almost extended.
It clearly isn't possible to maintain a level without training, so I put it down to trying harder or having accidentally done the right warm-up to recruit efficiently.
But I'm mystified. If I didn't really lose much over quite a long lay-off, I ought to be able to improve faster than I can when I'm training specifically for it. Past attempts have always ended with such slow progress that I get dispirited. I'm determined to bust out of this cycle of slow gains. So, experts, from where I am, how can I go forward to greater lock prowess? I can only train this in a park, so can't do the pulley thing to take weight off.