Obviously, plain old soap bars will not suffice to make a bath last for weeks or months. As I said pretty clearly, and you must have read, you cannot buy the good stuff.

You’re gonna need a lot more evidence than “it was explained to me”…

It’s trivially easy to find ancient soap recipes and revert them at hope. Or one can buy Aleppo soap, or Castilian soap from specialty markets.

It’s not like there’s some lost secret, or extinct ingredients - it’s soap, and it’s been a pretty simple thing to make for thousands of years.

You may try finding soap that will make a bath "last" for weeks. If you do find somebody claiming that, and actually give them your money, that is on you. I promise you will not get any of it.

This is starting to sound like a 'no true bath soap' fallacy.

You are ranging on the target now, but you are still off in the weeds. Don't give up yet!

Stuff's pretty good that I buy. And I bathe very infrequently.