Thanks for everyone who replied to my question.

From a brief examination, if I understand it correctly, KBART and ONIX
create normative standards for how holdings data should be represented,
which vendors (increasingly) follow.

This leads to three follow-up questions.

First, is there software to translate/normalize existing vendor lists from
vendors that have not yet adopted either of these standards into these
formats? I'm thinking of a collection of adapters or converters, perhaps.
Each would likely constitute small effort, but there would be benefits from
sharing development and maintenance.

Second, if holdings lists were provided in, or converted to, for instance
the KBART format, what software understands these formats to further
process them? In other words, is there immediate bang for the buck of
adopting these standards?

Third, unsurprisingly, these efforts arose in the managements of serials
because holdings there change frequently depending on purchase agreements,
etc. It is my understanding that eBooks are now posing similar collection
management challenges. Are there separate normative efforts for eBooks or
is it believed that efforts such as KBART/ONIX can encompass eBooks as well?

 - Godmar