I can share some insights about using bank feeds in QuickBooks Online.
The number of bank data that gets imported to your account will depend on your financial institution. Most of the banks download the last 90 days of transactions, and others go back as far as 24 months.
For the missing transactions, I suggest using the WebConnect feature. It allows you to manually add your banking data by downloading them on your bank's website and import to QuickBooks.
You can choose one of these formats to upload:
Comma-Separated Values (CSV)
QuickBooks Online (QBO)
In case you need the steps, here's how:
On the left panel, go to Banking.
Select an account.
Press the File upload option.
Also, I've attached some links below for your reference about using bank feeds: