Two pieces of evidence in relation to Caesar's Comentarii de Bello Gallico currently seem to suggest two different conclusions as to the authors veracity in reporting numbers.
One is from a comment posted on this forum:
Remember that Caesar's claims of building 25 miles of fortifications at Alesia (in barely 30 days) were regarded as hopeless exaggeration for nearly 2,000 years; until 25 miles of fortifications were discovered by archaelogists, just as described by Caesar.
The other is from German historian Raimund Schulz' book Feldherren, Krieger und Strategen: Krieg in der Antike von Achill bis Attila (see also here). Here is the relevant excerpt (translation by Google):
After a victorious battle against the Veneti - the first naval battle of the Romans in the Atlantic (footnote. W. Will, Caesar, Darmstadt, 2009, p 107) - he sailed in the year 54 with 600 load and 28 warships across the channel to a island called Britannia, from the contemporaries knew not much more than the early-modern Europe from Mexico or Peru before the conquest of Cortes and Pizarro. Even if the ship numbers are exaggerated - and 1944 has seen a larger fleet of the English Channel. It was the first amphibious expedition to the North Atlantic (footnote: W. Will, Caesar, Darmstadt, 2009, III the kind of ships of the fleet).
I assume that Wolfgang Will is citing further (primary) sources, but currently have now means of identifying those.
So here is my question: do we know the accuracy of quantitative evidence e.g. as to the size of battle groups or the circumference of protective walls as included by Caesar in his Comentarii de Bello Gallico? In particular, do we know the actual number of ships that he employed during the invasion of Britain in 54 BC from any independent sources? And is it plausible that Caesar would have helped his political causes substantially by inflating the size of opposing armies or (perhaps less likely) the size of his own fleet?