Mark Nicholls in the Oxford Dictionary of National Biography 2004 agrees with you In his article on Catesby he says Nicholls cites this to TNA PRO SP 14 216 136 although he doesn t explain exactly what that source is I can t trace it online except that Nicholls uses it again in his Strategy and Motivation in the Gunpowder Plot in The Historical Journal 50 2007 787 807