The Social Standards of the Global Reporting Initiative, available at https://www.globalreporting.org/standards/gri-standards-download-center/, can inform an appreciation of the People dimension of the Triple Bottom Line and are therefore worth a look.

PS: The Global Reporting Initiative, with details at https://www.globalreporting.org/, helps integrate sustainability considerations in the value chains of organisations. Established in 1997, the Global Reporting Initiative is an international, independent, not-for-profit, standards organization that promotes sustainability reporting as a way for organizations to become more sustainable by combining long-term profitability with ethical behavior, social justice, and environmental care. Over the last 22 years, starting at a time when little guidance existed, the Global Reporting Initiative has developed as a free public good a robust set of sustainability reporting guidelines to help businesses, governments, and other organizations adopt good practice in sustainability reporting.

For managers to evaluate subordinates` outcomes, you may utilize the OCB-I construct, as it is, as you said, an outcome of employees giving time to other people within the company.

Have you looked at the work of Karl-Eric Sveiby and of Scadia with regard to intangible asset accounting in the late twentieth centruy?

https://www.sveiby.com/files/pdf/intangiblemethods.pdf