When changing accounting software, whether as of a fiscal year close or even mid tax year the important thing to enter as BEGINNING balances are ALL the balances from your Balance Sheet as of that date. This includes bank balances, loan balances, asset values, etc. The WIP accounts have specific 12/31 balances. That is what you enter since the individual transactions are in last year's books.
Example, you have Project Jones House and you incurred $123,456.78 in expenditures that due to the tax rules cannot be deducted from income until house is sold -that as you know is a WIP and despite there being 500 individual transactions during 2020 as of end of last year its balance sheet value as a current asset is $123,456.78 and that is what you enter as a 1/1 beginning balance.
Every beginning balance , after posting to its individual account, then posts to a special one time use equity account called Opening Balance Equity. This, in essence, is the value of your business on the date you begin the new year (or end the old)
If you are just now creating the accounts with beginning balances you can and should enter those beginning balances with the beginning dates as prompted when setting them up. If you crested the accounts previously with no beginning balances you can use a Journal Entry to add all the starting balances and the total offset, Debit or credit, goes to OBE.
