Well, I am glad you asked.
The first thing that will matter is where you bank and what type of account you have. It also matters if you are adding through Open Banking. There is no real industry standard so your Barclays Credit Card and a Sainsbury's Bank current account can vary quite a lot. A general rule is that credit cards can go back in time less and current accounts more. Open Banking Supported Providers get more than accounts that are updated using token sharing (Yodlee)
We will always try and request 90 days transaction history for credit cards and for everything else we will request 12 months of ransactions history. With the provision of Open Banking this may increase. (So we'll let you know when we know).
Unfortunately you can't add any historic data through a manual transfer