FWIW, we’ve just uploaded our OSS/BSS Interface Specification Template onto the Passionate About OSS download page, which includes lots of worked examples.
You can grab it here and start updating for your OSS/BSS interfaces:
https://passionateaboutoss.com/product/oss-bss-interface-specification-template
We’d love to hear your comments if you have other suggestions for what else should be included.