Access to account numbers after death

Sadly Ive recently had to go through this process for someone without a will and i havent had a single account number to help me. All ive had to go on is the institution where i know there are investments, its actually been very simple, so simple in fact its been emotionally upsetting to see accounts closed so quick but thats another story.
One bank even let me close the account over the phone.

i would recommend writing down where you have squirreled away savings as it is entirely possible i have missed some.