Display the address tab and find the addresses with balance, those are the addresses that should be checked on blockexplorer sites.
Only if those addresses have not been touched since before <insert fork date here>
If the OP has been sending/receiving transactions since the forks, it is very likely that coins are currently contained in change addresses or receive addresses that are different from the ones in use prior to the forks. So, looking at the current balance of a given address is likely to be inaccurate.
Even the OP seems to realise this:
I need to see which addresses contained coins 1 year ago at date x.
all coins from my wallet were moved already to a different address
my wallet balance is 0 now
Given all the BTC has already moved... a mass export/import of private keys poses no real security risk to their current holdings.
Using the "electrum" forks of the larger forks is probably the easiest way to get their coins out.Simply make several copies of the Electrum "default_wallet" (or whatever wallet file you've been using) and open it using the appropriate fork wallet. Your "fork coins" will magically appear!
For fork coins without an electrum fork... you'll need to dump the private keys from Electrum and load them into a fork coin wallet.