This is a Fermi estimate. Some days, a monk may write a veritable novel in their journal. Other days, they might just doodle. A monk might find writing boring and do their journals entirely in drawn form. Another reincarnation of the same monk may do their journals calligraphically. A first generation monk may be literate in their native language but completely illiterate in the language the monks prefer; subsequent generations may need to build translation guides and then hope even further iterations get use of them. Plus, studying a journal might mean studying the pre-translated e-book version, it might mean transcribing a physical version onto the e-book, or it might mean learning how to preserve old texts and then meticulously using that treatment process on centuries-old journals that fell under a desk a generation before.
Plus, both monasteries and Slow Caravans are veritably self-sustaining, independent cities, growing their own food, making their own fabric and paper, synthesizing their own polymers, refining their own metals, everything their technology requires for maintenance. Some days, a monk might be out working from sunrise to sunset, only stopping for meals and bodily functions. They find a stopping place in their work, shower (or otherwise clean themselves) then pass out in their bunk with nary a word in their journal. Maybe a teenager is weighing the pros and cons of sticking with the monastery when a buddy in the same boat wakes them up in the middle of the night for some typical teenager stuff, waking up late the next morning. Maybe a missionary has the misfortune of visiting a city that's under siege and gets killed, or a Slow Caravan gets captured by a raiding army short on supplies.
This story presents the Platonic Ideal version of the Immortal Monks. In reality, life would get in the way quite a bit and it'd force some cultural drift.