GB Wattses Underprints - New Discovery?

Protective underprints, the printing of a company name on the reverse of the stamps, were used to prevent theft in the same manner as perfins.

Although predominantly a Victorian fad, two firms used underprints in Great Britain from 1904 to 1915.  The underprints were done over the gum, so excessive soaking of used stamps obliterates the underprint. Accordingly, they are scarce.

S&J Watts, a drapery firm from Manchester, used an underprint on the stamps of both King Edward VII and King George V. These underprints are listed in the Stanley Gibbons Great Britain Specialised Catalogue Volume 2.

Whilst soaking a batch of KGV on paper, I found these, somewhat poor, KGV definitives

Ready to consign them to the seconds bin, I turned them over and saw this