This looks like a 1928 set offered in a 1927 Proof Set Box.

[ozjohn]

 I have a 1927 set in an identical box even down to the remains of tape on the back of the box. I don't know if any 1928 proof sets were ever issued but this looks like a cobbled together set of  1928 coins presented in a 1927 proof set box to trap the unwary at a high price.