It should be checked if the composer "Castilho", represented with one work in the manuscript P-Cug MJ1, preserved at the Biblioteca Geral da Universidade de Coimbra, was one of the Spanish composers Diego del Castillo or his brother Bernardo Clavijo del Castillo. Paulo Estudante (2006), p. 654, annotated: "For the moment it is impossible to determine with certainty to which one of these musicians the ‘Castilho’ indication refers (if, indeed, it is either). However, in contemporary documents concerning the two brothers, it is clear that the younger brother is almost always referred to as ‘Clavijo’ or ‘Bernardo Clavijo’. Fragile as this argument may be, it is possible that the first work notated in P-Cug MJ1 is by Diego del Castillo. If so, it would be his first work known to modern musicology."