The damage to the basal plate seems to have stimulated production of lots of daughter bulbs. I think if you had the time - surgery with a craft knife/razor blade, cut into pieces to access/cut away the decaying centre, soak in a fungicide then pot up any healthy pieces in a very free draining mix or just damp vermiculite as if you were twinscaling them.
I bought a bulb of one of the new "Amaryllis" (Hippeastrum) Sonatini cultivars 'Eyecatcher' at my local Morrisons yesterday which seemed a bargain at £2 until I got it home and opened the packet;
I've given up being shocked at how appalling the quality of bulbs from very many suppliers is (I've just received some Nerines & Lycoris from a well-known supplier of Dutch bulbs which are in a similar state). I was busy yesterday so with the 'Eyecatcher' bulb I just took off as much as I could of the rotting outer scales, sprayed with Fungus Clear and potted into a gritty mix and will watch to see if the bulb is able to recover but I am considering doing some trials of different rescue techniques/fungicides with some of the other duff bulbs. (also while in Morrisons I bought a mould treatment designed for showers etc as my house has very beautiful cast iron windows which unfortunately don't currently look beautiful as they are dripping with condensation and attracting a whole ecosystem of assorted moulds. But once I read the instructions on the product it says don't use on metal so I was toying with the idea of trying it on the bulbs instead - although obviously aware that this would be in breach of all sorts of rules and regulations...)