Lambda "1" = Stoichiometric, regardless of the fuel being used.
At Lambda 1, every fuel particle has found a matching air particle to bond with, meaning there's no excess of either fuel nor air in the mixture.

All of the known fuel AFR-numbers are just calculated from the Lambda-number by 'known' fuel-stoich-numbers.

When mixing fuels, the stoich-number becomes a 'best guess', so it's then better to stick to Lambda-readings because they don't change.