I can only comment on the 'black earth' bit. As it rots down it does lose all of the obvious twiggy or staw-like bits. It is still very useful at this stage and probably better for things like carrots, as a lot of the goodness will have washed out with the rain. Strong manure is bad for most plants and can scorch roots and do more harm than good. Slugs will be drawn to manure to digest the less rotted bits.

I've never understood why so many gardeners have this obsession with 'digging in' manure when all it does is changes the soil structure for the worse and creates conditions where roots have problems, as with the splitting of carrots you mention.
In nature, 'compost' forms when leaf litter and other materials fall to the surface. In fact, most plants produce feeding roots in the very top layer of the soil, and thicker roots for water which go deeper. So putting the 'feed' deep in the soil is just a waste, apart from increasing a little the water holding capacity. I always apply compost as a surface mulch and find this works far better. Carrots won't be affected (you pull the mulch back for drills when sowing and push it back around the growing plants), it helps suppress weeds, and you don't get immediate breakdown into nitrogen which causes the leafy growth in leguminous plants as you have observed.
What's even better is that over the autumn and winter, it promotes worm activity and the worms do most of the work in incorporating the manure into the soil.
It would be interesting to hear what your allotment society think about this when you have your meeting.