That is simply not true.

Where are you getting this stuff?  It's rampant misinformation.

In fact, BIP39 only uses the first four letters of each word, so to "forgot one letter" might very well not be that big of a deal in the first place. 

On top of that, you can use sparrow wallet to insert your seed phrase (I'd recommend doing it offline) and you only need input the first letter of each seed word to get a drop down of all possibilities.  Then you can choose from that list to help you remember.

And further, even if you still "forgot one letter" you'd get endless chances to get it right.  It's not like you only get three tries and the blockchain locks your wallet or something.  The blockchain doesn't care how many times you try.

So please, try to make sure you've got your facts straight before you present such incorrect claims as statement of fact. The idea that forgetting just one letter of your seed means you can't access your wallet is patently untrue.  It's simply not that rigid.