Comment by hereonout2

It is interesting to know! My assumption would be it's technical or scientific publications, maybe things like the Springer back catalog (assuming they've not already licensed these). Some of these are "rare" as in they are essentially published PHD theses with very little in the way of sales / print runs.

Of course I could be wrong and they are destroying 14th century monastic scrolls or out of print Mills & Boon editions.