If I leave my surplus funds in the same bank account to use for the next election, can I still file my final C-4 for this election?
Do not file the final C4 until the cash on hand amount is zero.
Either file a C1 registering the surplus funds account and report a campaign expenditure showing the transfer to the surplus funds account and then file the final C4 for the campaign or
File a C1 registering a campaign for the next election and you can leave the funds in the same bank account, but they can only be used for the new campaign and are no longer surplus funds. You can then report the expenditure to the new campaign and file the final C4 report.