I don’t know if this is useful info but it helped for me.
It was my first year growing shallots from Aldi (Golden Gourmet, Red Sun) As you would expect they were super cheap, but I notice some white mould growing on some of them.
So I planted my shallots first in pots in the green house, when it came to planting time I gave each shallot a good tug. The duds came out very easily (I don’t even compost these as that might spread the contagion).
The other advantage is that the I don’t get nasty gaps in my rows, due to fatalities.
I plan on saving the biggest shallots for growing next year, and I shall be repeating this process.