Well, you said it! Much of the time when Chevallier barley malt was king, much mashing was still done by the old multiple mash system (no sparge) and at much higher temperatures; not "single infusion". And, most importantly, for much longer and probably with much longer periods of mixing ("mashing"!).
And you probably used a dextrin happy yeast, even before adding "I'll eat anything" "Brett".
We weren't always so lazy (says me, the prime example of laziness) as to expect 60 minutes of mash will be enough.
[EDIT: Actually, it had always troubled me that Victorians got lowish FGs from high-temperature mashes, I hadn't considered their Brett infected wooden casks until unthinkingly writing out the above response.]