I soaked the birded bits, and the solid matter has come away. Now soaking in more soap solution, but after talking to the Vulpex man - the creator and developer, not a salesman - I am ordering some of his stuff. Given the possible fragility of some of these pieces, particularly the lace, I really don't want them soaking for days and days, and a couple of soaks in ordinary detergent doesn't seem to be shifting the muck.
I'll send him a cheque, and do a comparative test, using the stuff I haven't tackled yet. If we get a miracle cure, then I can re-do the done-in-Ecover bits and get the result I'd like. The good thing about this stuff is that it leaves no residue, and the solution can be re-used lots of times, so though it's expensive, I will get a lot of use out of it.
This was no hard sell: he was most keen that I try the little 100ml bottle, but in solution that wouldn't even cover the smallest garment. I shall see how this works, anyway, and continue to document the process.