Wam,
The complex i.e. the construction of the baths and library building was begun in Victoria's time, so quite obviously they had been designed before the first spade was inserted....this by any logical architectural norm makes them Victorian...the last part was ''finished'' fit for purpose and opening around the date you mentioned. By your rationale, a building or complex designed, whether begun or not, with the last part at least, begun in the 1990s, is 21st Century architecture......the Marines at least may be pleased to learn of that.