The RIBA Guide to its Archive and History (1986) has a section on the "Statutory registration of architects" with a bibliography extending from a draft bill of 1887 to one of 1969. The Guide's section on "Education" records the setting up in 1904 of the RIBA Board of Architectural Education, and the system by which any school which applied for recognition, whose syllabus was approved by the Board and whose examinations were conducted by an approved external examiner, and whose standard of attainment was guaranteed by periodical inspections by a "Visiting Board" from the BAE, could be placed on the list of "recognized schools" and its successful students could qualify for exemption from RIBA examinations.

Answer this question, if possible (if impossible, reply "unanswerable"): When does the Royal Institute's Guide indicate the last RIBA Board was established?
unanswerable