Wachsmuth (apud Bader189032n. 38) proposed a variation on this. He assumed that a marginal gloss nimirum Fabii est was interpolated into a putative original text of quod in Pictoris.
Freyburger and Scheid (2004) also accept nimirum in as is evident from their French translation but they use the text of Pease as its basis and make no comment on the textual question in their commentary on this passage.
E.g. Frier199971. There are other reasons why Cicero might have chosen to lead off with Cato. He was after all the most famous of the three and wrote in Latin unlike Fabius. Cicero does list these and other historians chronologically at Leg. 1.6 where he also elaborates on Cato alone: si aut ad Fabium aut ad eum qui tibi semper in ore est Catonem aut ad Pisonem aut ad Fannium aut ad Vennonium uenias; for the elaboration on Cato in this passage see also Cic. Brut. 66: iam vero Origines eius quem florem aut quod lumen eloquentiae habent and Dyck 2004 75 ad loc. Momigliano (1990 91) assumes that Cicero refers to the Latin annals in De legibus but there is no compelling reason to do so.