Documentation of LMS capabilities?

Is there any documentation out there for what LTI capabilities the LMS's actually support, and in what contexts? Something like the certification process, but showing details of the specific capabilities and how they can be used?

There are lot of optional capabilities in the spec, and even for the required specs LMSs seem to have interpreted how things should work quite differently. It'd be super helpful for tools to have a simple reference for these things.

An example is the "multiple line items for one launch" / programmatic line item capability of the Assignment and Grade Service. Some certified compliant LMSs don't seem to support this at all, while others partially support it or only support it for certain launches from certain contexts. And without getting my hands on the LMS and testing extensively, I have no way to know the specifics.

Sorry if this comes off as a rant, but I feel like the point of the LTI standards was so that tools can just "work" with all the LMSs without having to custom-build an integration for each, and with LTI 1.3 I feel like I'm having to learn and develop around the capabilities of each LMS, without the benefit of any documentation.