Hi Quinn K,
Thanks for that - it worked! What's interesting is that I hadn't seen the download button because every bundle has two pages on Itch, but only one of them lets you sort the games A-Z, so that is the one I always used (partly because I wanted to add all the games to a collection "Not Yet Played", and because there is no automated way to do it, I had to do each one manually - requiring multiple days, and therefore noting what letter of the alphabet I was up to). So it turns out you only see a download option if you use the other bundle page, that doesn't have sorting options. Here's a screenshot of each:
A good example of how the Itch interface is often very confusing! Having two different pages for each bundle instead of one, for example.
I did ask Itch Support about this twice. Presumably they could have given the same answer as you, but they never replied to those emails (or any others I sent in the last few years) which is a shame, as I feel more of an affiliation to Itch than to GOG or Steam.
Thanks for taking the time to explain this, I'll have a look at your pdf and the other things I couldn't access in bundles. :-) Hopefully this post will be useful to anyone else with this issue.
Best wishes, Karl