This came from Mrs M, a national of Lebanon who made a SET(M) application for herself and SET(O) applications for 2 children who turned 18yo by the time of applying for an ILR.
In this case the main applicant was married to a British citizen and had a Spouse Entry Clearance under the old Rules (ie issued before 9 July 2012). So it was a straightforward SET(M) application. However, the 2 children of the main applicant were issued with dependent visas at the time of entry to the UK and now, by the time of ILR application, they turned 18 yo. It meant we could not include them in the SET(M) application as dependents. Instead we had to add a SET(O) application for each child, at the same time as the main SET(M) application, as well as full SET(O) fee.