Originally Posted by sylla1
If you may be aware of any recent quellenforschung that may back such categorical assertion, please share it with us,
Conversely, if you may not be aware of the centuries-long academic study on the sources of Livius' work, this would be a good chance to review it.
Even in Wikipedia you might find some useful stuff on this topic.
here you have from wikipedia:
For the first decade, Livy perused the works of a group of historians in or near his own times, who, rightly or wrongly, have been called "the [ame="http://en.wikipedia.org/wiki/Annalists"]annalists[/ame]." Some twelve historians in this category are named by Livy in Book I as sources on the monarchy.
In order of time interval backward from Livy they are: Gaius [ame="http://en.wikipedia.org/wiki/Licinius_Macer"]Licinius Macer[/ame], [ame="http://en.wikipedia.org/wiki/Quintus_Claudius_Quadrigarius"]Quintus Claudius Quadrigarius[/ame], [ame="http://en.wikipedia.org/wiki/Valerius_Antias"]Valerius Antias[/ame], Gnaius Gellius, Gaius Sempronius Tuditanus (consul 129 BC)
, [ame="http://en.wikipedia.org/wiki/Lucius_Cassius_Hemina"]Lucius Cassius Hemina[/ame], [ame="http://en.wikipedia.org/wiki/Lucius_Calpurnius_Piso"]Lucius Calpurnius Piso[/ame], Aulus Postumius Albinus (consul 151 BC)
, Gaius Acilius Glabrio, [ame="http://en.wikipedia.org/wiki/Cato_the_Elder"]Marcus Porcius Cato[/ame], [ame="http://en.wikipedia.org/wiki/Lucius_Cincius_Alimentus"]Lucius Cincius Alimentus[/ame], [ame="http://en.wikipedia.org/wiki/Quintus_Fabius_Pictor"]Quintus Fabius Pictor[/ame]. Elsewhere he mentions [ame="http://en.wikipedia.org/wiki/Sempronius_Asellio"]Sempronius Asellio[/ame]. Macer, the latest of these, died in 66 BCE. Fabius, the earliest, fought in the Gallic War of 225 BCE.
Livy's sources were by no means confined to the annalists. Other historians of his times mention documents still extant then dating as far back as the kingship: treaties between [ame="http://en.wikipedia.org/wiki/Servius_Tullius"]Servius Tullius[/ame] and the [ame="http://en.wikipedia.org/wiki/Latins"]Latins[/ame]; [ame="http://en.wikipedia.org/wiki/Lucius_Tarquinius_Superbus"]Lucius Tarquinius Superbus[/ame] and [ame="http://en.wikipedia.org/wiki/Gabii"]Gabii[/ame]; three between Rome and [ame="http://en.wikipedia.org/wiki/Carthage"]Carthage[/ame]; Cassius and the Latins, 493 BC, which was engraved in bronze. In addition the [ame="http://en.wikipedia.org/wiki/Pontifex_Maximus"]Pontifex Maximus[/ame] kept the [ame="http://en.wikipedia.org/wiki/Annales_Maximi"]Annales Maximi[/ame] (yearly events) on display in his house, the [ame="http://en.wikipedia.org/wiki/Roman_censor"]censors[/ame] kept the Commentarii Censorum, the [ame="http://en.wikipedia.org/wiki/Praetor"]praetors[/ame] kept their own records, the [ame="http://en.wikipedia.org/wiki/Commentarii"]Commentarii[/ame] [ame="http://en.wikipedia.org/wiki/College_of_Pontiffs"]Pontificum[/ame] and Libri Augurales were available as well as all the laws on stone or brass; the [ame="http://en.wikipedia.org/wiki/Fasti"]fasti[/ame] (list of magistrates) and the [ame="http://en.wikipedia.org/wiki/Linen_Rolls"]Libri Lintei[/ame], historical records kept in the temple of Juno [ame="http://en.wikipedia.org/wiki/Moneta"]Moneta[/ame].