FYI, those are under the premise that the actual password is simply "the date".
Not easy if it's just a clue left by your father.

For example: my easily-accessible written account list doesn't have the actual password but a clue for me to remember which of my common passwords to use.

But at least if you try to bruteforce, you can deduce that the password is not simply a date if it exhausted the search.
That's not doable by hand though since you'll be typing each of the possible millions of combinations manually so you'll need the "stuff" to do that.
At least use the suggested "open-source" tool BTCRecover which you can audit the code.