Speaking as someone who has spent a lot of time studying the titles this past week, 'Sylvester Daggerwood' sticks out as an interesting case. Written by George Colman (a very prolific playwright amongst our playbill collections it seems), Godwin's Diary (http://godwindiary.bodleian.ox.ac.uk/dramatists/col01.html) has SD down as a farce adapted from Colman's earlier play: 'His Hay at the Old Market' (1795). From the titles data, however, we also have: 'Silvester Daggerwood; Or, Margate Theatricals', 'Sylvester Daggerwood: Or, the Dunstable Actor' and several plain 'Margate Theatricals', which could be related or something entirely different.
The evolution of subtitles over time is a fascinating topic -- has anyone noticed any other plays with changing subtitles in their travels across the collection?