As Hyphen Press explain, hardbacks used invariably to be bound properly, but now they are often simply paperbacks between boards.¹ Signalling alone as above is

As Hyphen Press explain, hardbacks used invariably to be bound properly, but now they are often simply paperbacks between boards.¹ Signalling alone as above is the correct explanation. Cloth books can have practical advantages, such as the possibility of rebinding, but modern hardbacks mostly lack them. 1. https://hyphenpress.co.uk/journal/article/bookbinding_survey https://hyphenpress.co.uk/journal/article/bookbinding_survey