Some posters have said that IS allows keywords not in the CV - but I can't see a way to do that with DeepMeta.   It only allows words from the CV.

No you can add free keywords on top in DM. Mine are already in the IPTC. If keywords are not in the CV, they are colored blue in DM, but they still get accepted.

An example is the word "emo" (goth lifestyle, with a lighter touch). It always colors blue in DM but it's searchable as such on iStock. Just type in the search box for "emo" : Over 1,000 results. Click here.
It's a bit of a niche since 4 of my shots are in the top 6. And by the way, you can see that exclusives in general are not pimped in the search results since I'm not exclusive.

Of course, you need to use that opportunity very wisely, and only if you are sure. I never use it for plain English or common terms.

I heard that there is a forum section on iStock where new terms for the CV can be suggested. Do the iStockologists know exactly where?

I think the non CV keywords show up in DeepMeta with a blue background rather than a green one with various disambiguation options. So you can add your own keywords/phrases, they just won't be translated into other languages by the search engine

That's quite OK since "emo" is a global word, it's used in all languages I know.

Yes, I've had that problem too. You can use a phrase, eg audio track, but it's probably best to email keywords and ask for the additional meaning to be added to the options.