Mark,
Currently, my account history in FM only goes back to 2017 (as far back as TD Ameritrade would download from the OFX server when I started using FM -- or at least since the last time I screwed up my portfolios so badly that I had to re-create them!) I am entering older history from paper statements, as I do not trade too often, and this seemed easier than trying to download transactions to CSV and untangle all the importing issues. More importantly, this method makes it easier for me to check after I enter each statement to verify that all my shares and balances are right.
What I would like to do is create a dummy portfolio for each account and enter my older account history into it; verify that the resulting balances match the starting balances that were downloaded from TD when I began using FM; delete the starting balance entry from the current portfolio; and copy and paste the historical transactions for each investment from my dummy portfolio into the current portfolio that contains the recent account history.
Will this work? It seems that it should, except perhaps that if I copy and paste transactions into an investment, it might create new entries in the default cash account (which would then be duplicated when I copy and paste transactions from the "dummy" default cash account to the more recent default cash account. Would that happen? What is the best way to accomplish what I'm trying to do? I imagine I'm far from the first to start using FM for a while, and then decide to add older account history later.