I think it may not the same Robert Harley who married Joan Corbet dau. of Sir Robert Corbet, parents of Alice (m. c.1375 Hamon Peshale d. c.1398).
According to History of Parliament Sir Robert Corbet was born c.1354-1417, the above Robert Harley would of been born before Sir Robert father of Joan Corbet. I can't see a Robert Harley b. 1276 as having a dau. Alice who m. c.1375.