[stumped]

i explained how the client cannot possibly be the cache
i will walk you though it again
i retrieved a book from content server to calibre companion on tablet A
i spotted an error when reading so I edited the book back on the PC, using sicgil, thus updating the copy in calibre library - on the C drive , in default location
then I took tablet B, which was OFF, turned it ON, and used it to get the same book via the same connection. NB this table was off until AFTER i had edited the book, and has never had the book on it.
that tablet - call it tablet B received the old - un-edited copy from the content server
so it cannot be the client - the client was never on until after the book had been edited

I observed this with other books , some weeks ago, and posted about it then, but I got a blanket denial that the content server does not and cannot cache

so i set out steps to reproduce the problem in my previous post,
someone needs to take those and prove or disprove my claim on other equipment
it is a simple test which will only take a couple of minutes.

meanwhile I confirmed AGAIN, that if i shut down calibre and remove book from tablets A& B, then re-acquire it, I then get the updated version

[ last time around, I went even further, I did another edit, removed book from devices, re-acquired it a 3rd time, and did NOT get the most recent edit.. to get the most recent edit I have to stop / start calibre- stop /starting apps / clearing app caches, or even power cycling tablets in between content fetches makes no difference.

clearly ( to me ) content server or related processes are holding stuff in RAM and re-using that to fulfill requests. [ until such time as either calibre is stopped/ started, or cache is overwritten by other requests from server .)
I searched calibre app data and saw nothing that could be a cached book

ps you asked about network
the complete path is :PC with calibre library is wired to a GB switch, which is wired to my router
the tablets use wifi to reach an access point [ asus R56U ]which also wired to the same router[ virginmedia hub]
so the tablet app - calibre companion - sees the content server at local lan address 192.168.0.72 and asks for content to download from there. both tablets do this.

PS yet more confimation. if I mirror calibre library to dropbox then tell CC to get book from dropbox, it always gets the version that was most recently mirrored into dropbox. so I could edit book, sync to dropbox, get from dropbox, and always get the most recent version. it is only when I get from calibre content server , without stopping calibre, that i get previous cached versions