Hi, Adrian! Thanks for offering to help.
I will hope to use the right words.
When I click on the download link (either for the full .ai or .svg archie with the .sit extension) I am given the choice to open with StuffItExpander or to Save the File. I chose "Open with StuffIt".
It downloads, then a text file opens with the Mac program TextEdit. The text file is full of gobbledy-gook characters.
I cannot see any other options to expand the archive. In the folder where it was saved, it is listed as only one file with a .sit extension and I cannot open it or expand it with anything I've tried.
The reason I tried the .ai version after the .svg (.sit) failed was that Inkscape has an option to save as .ai so I thought it might open them as well. I have not confirmed this.
But the StuffIt expander did not open this download either.
So, no, I have not been able to extract the collection at all. StuffIt will not extract the collection(s) and I don't know what else to try.
I am using a new MacBook Pro.
Thanks for your help. I might be missing something very obvious!