Does anyone remember when they changed the way docs were stored in the account? I looked into my a count and all docs start at 2011. But I know that I have send many before that via the email option. I can't recall when the send to kindle add on thingie came about, but I used to use the email address back in the day. My docs should go back for as long as I had kindles, 2008.
As it shows now since 2011, I am not above that threshold yet mentioned in the OP. I don't use calibre for those. Its mostly recipes and things like that and some books I bought elsewhere. The kindle cloud is much more easy accessible to me than calibre. Its always there, while calibre is on a computer I'd have to start up first and all that. I only go into it every 2 months or so to backup my purchases from amazon, that is about it. I don't use it to send stuff to my kindles either. So I'll have to figure out something if that is the max number. If that happens, I'll contact amazon. The rate I am going I should be there within the next 1-2 years.