[firecall]

My strategy would be to go for redundancy:

The physical book can contain a QR Code, Barcode, printed URL and so on, that’s correct at the time of print.

But then leave hints on how to search and find the book online if those resources are not available.

Such as a promise to list the book with your Author name, book title, ISBN and so on.

Then replicate the content across the internet, and try to cross link to all the resources.

The only thing you can really trust is your own domain name, so that has to be the base right now.