A support email came in recently asking if Remembary downloads tweets "retrospectively" or if it just captures new tweets going forward from installation. I tried responding but the email they submitted bounced back. So, if they're reading this - and for anyone else who would like to know:
Yes, Remembary can fetch your tweet history.
Tap on "Journal Prefs" and in the popover that comes up, tap on the "Get All Tweet History" button. It will send repeated requests to Twitter, eventually getting all of your past tweets, up to a Twitter-defined limit of 3500.
Note that occasionally Twitter will flake out before sending all of the tweet history, but you can just hit the button another time and try again. Remembary is clever enough to not store duplicate tweets.
I found this really handy in using Remembary myself - I was able to get all of my tweets from the last year and a half, which really helped me fill in the gaps in my older diary entries.
By the way , with RSS feeds, Remembary will download as many older feed items as the feed provides - it depends on the feed. I've seen some feeds that only show items from today, while others go back for years. Remembary will pull in as much as it can get - there are no built-in limits.