I'm not sure where the documentation you found suggests this

The Yocto Project documentation: https://docs.yoctoproject.org/ref-manual/variables.html#term-SPDX_IMAGE_SUPPLIER contains almost the same example:

MY_COMPANY_name = "Acme Corp"
MY_COMPANY_type = "organization"
SPDX_IMAGE_SUPPLIER = "MY_COMPANY"
SPDX_SDK_SUPPLIER = "MY_COMPANY"

the support for this is already implemented by undocumented `_ref` suffix, so maybe documentation should be changed instead.
Though `_ref` suffix if I'm reading code correctly allows for infinite chaining e.g:

SPDX_IMAGE_SUPPLIER_ref = "MY_COMPANY1"

MY_COMPANY1_ref = "MY_COMPANY2"

MY_COMPANY2_name = "Acme Corp

but the values for any base variable are suffixes always appended to that base variable

SPDX_IMAGE_SUPPLIER = "MY_COMPANY"
SPDX_IMAGE_SUPPLIER_MY_COMPANY_name = "CCCC"
SPDX_IMAGE_SUPPLIER_MY_COMPANY_type = "organization"

This one I don't think is mentioned anywhere, and also doesn't work. Maybe you meant SPDX_AUTHORS which has this syntax:

SPDX_AUTHORS ??= "openembedded"
SPDX_AUTHORS[doc] = "A space separated list of the document authors. Each item \
is used to name a base variable like SPDX_AUTHORS_<AUTHOR> that \
describes the author."
SPDX_AUTHORS_openembedded_name = "OpenEmbedded"
SPDX_AUTHORS_openembedded_type = "organization"