The publishers were aware of the error on the spine and I think that has been fixed, not sure about your second point.

Received the 3rd print of this book and still no name on the spine and dust jacket is still of poor quality. Got it all damaged around corners.

Do you know if there exists a study somewhere of how Christopher Tolkien paraphrased his father extensively in the UT? I'm thinking in particular of certain long passages at the end of the text about Aldarion and Erendis, or those about Galadriel, which are indicated in the publisher's (so Christopher's) font, but which are relatively close in style to Tolkien without being indicated in quotation marks.

See these two notes in the beginning of the book.

in The Further Course of the Narrative of 'Aldarion and Erendis', pp. 215 ff. ... both author and editor are in the smaller type, with citations from the author indented

This movement away from a staccato annalistic style in the present tense into fullblown narrative was however very gradual, as the writing of the outline progressed; and in the earlier part of the story I have rewritten much of the material in the attempt to give some degree of stylistic homogeneity throughout its course. This rewriting is entirely a matter of wording, and never alters meaning or introduces unauthentic
elements.

Of course I read these notes, but all is in the "This rewriting is entirely a matter of wording" sentence. Of course Christopher didn't alter the global meaning, but I'm interested in his specific wording compare to his father's, if this exists (it probably doesn't, for I guess these manuscripts never where published per se, but who knows...).

Instead, or to complete my request, are there any books where some of the UT manuscripts have been exhibited ?

A lot of unused text for Hunt for the Ring is in the Reader's Companion.

Unused text from a bunch of the other tales are in Nature of Middle-earth.

There aren't a lot of manuscript reproductions of the material, but there was a page of The Line of Elros in Maker of Middle-earth.

Do we know if there are any differences between the WM (978-0358448921) and HC (978-0008387952) editions of the trade hardback?

Their listed size is slightly different, I have most of my trade hardbacks as HC editions but the WM is easier to get here & Blackwells keeps damaging the HC editions they are sending.