Why not just put it into the garden, or whatever you do with your compost?

The nitrogen, potassium, phosphorus, calcium etc. that you want from your compost are still there. Composting is mainly a matter of using bacteria to break complex organic stuff down into simpler organic stuff that plant roots can grab. That has been largely accomplished. Further breaking-down will be done by the little beasties in the soil once the compost is added, and there is no shortage of those.

Here is a link that might be useful: more on composting

inert

I guess if you are using it for brewing worm tea then inert would matter.

The bacteria have probably done what they need to with the vermicompost by now.

Use it as normal.

If you do not need it right now then using it to cover the vermicompost bin is always good so that there is some friendly material for the worms.

No worries. Vermicompost that is six months old (or whatever you mean by "from last winter") is just fine to add to soil and will help plants just the same as freshly harvested stuff.