You need to deal with BOTH the check records and the invoice records in apopnfil, apopnhst, apdisfil and bbopnfil if you are using bankbook (if you want to DELETE the zero balanace records). You need to do both the invoice and the payment transactions, otherwise you'll leave payment records with no invoices which will create yet another problem.
Exact's recommendation was improper because you did really get these invoices and really did pay them, therefore they should not be deleted.
If you use open item load to change the invoice dates to the correct dates, you will have good info in apopnfil & apopnhst. It sounds like the check date was correct, so no worry in bankbook. That leaves apdisfil to correct. Did you post the 2020 voucher transactions to GL at some point & correct the dates in GL or in a GL transaction session? You can verify if ever posted by running AP distribution to GL including interfaced transactions & see if there is an * next to the transactions. If so, you probably have corrected in GL already. If so, I would just leave it alone since you've documented the original activity and the correction in your system of record, which is better if you ever have to deal with an audit. Taking records out through the back door leaves no audit trails. Unless you document what you've done, you can create suspicion about the validity of your accounting records.
If you do use open item load to change the invoice dates, you should run reset fully paid items, reset vendor account balances and age vendor accounts. Double check your open item reports to be sure the transactions now have the correct dates. With the correct dates, these transactions can now be purged if needed since the records net to zero and are before a particular date you specify on the purge.