Well I have searched the internet and nobody seems to have had the same situation I have, of overwintering shallots that divided but didn't bulb.
Main problem is, I planted them at the spacing which would be good if you expected a single bulb per seed. So they are obviously overcrowded, and today I moved them by clumps to give them at least a decent spacing between rows. First pic is early may as they're coming up through the mulch of their own leaves. Second pic after spacing. Some are oddly bent that is because they grew up and raised the mulch with their top leaves. Those that were protected by their own mulching also avoided the attentions of Mrs. Grouse, who has nipped really a lot of them, to my surprise. (and also nipped a few of my garlic).
There is a fair bit of variation in these shallots, some is pretty certainly genetic - some have a lot of red on the stems which makes the lower part look olive-brown, some have no red at all. So it will be interesting to see what comes - I hope they all produce bulbs. I couldn't space them any further apart as there is nowhere to put them except the same bed, which last summer also hosted some leeks.
So my big worry now is... have I attracted onion maggot flies? And if so, what should I do? As I was working on the transplanting today, there were a lot of flies pitching on the shallots. Some large, some small, it is hard to know what kind of flies they are or why so many would be on these plants and not on anything else. (none around the garlic or chives or perennial green onions etc). Could it be they are attracted by the sap because of the damage by the grouse? Or are they the maggot kind of flies and getting ready to destroy what I have planted?
Any suggestions about preventive measures? Organic only, I don't use any chemicals.