A couple of points I want to make for clarity here.
While I found the article very interesting as well, we need to all remember that the article is a translation from French, so it is possible that some inaccuracies due to translation can occur. Please be sure to read all of the other chapters when you can. There's a lot of good work and information there.
Regarding crossing between Sempervivum and Jovibarba, there is a nomenclature issue to keep in mind. Some authorities regard Jovibarba as not a species, but rather a subset of Sempervivum. So when reading discussions regarding Sempervivum X Jovibarba heuffelii crosses, please keep in mind that the "Sempervivum" involved could conceivably be another "Jovibarba" according to how the author is using the nomenclature terms. I am not current on what the proper nomenclature is these days, but always try to watch out for that possible ambiguity. Not my area of specialization, just being a hobbyist. I try as much as possible to go with correct names, but as a hobbyist, also try to use the best name I can to identity the plant in the hobby.
Regarding Green Gables, I had that a few years back from a trade, but all of the rosettes bloomed out without making any offsets. As I recall, the plant was a bit unusual in that the blooming occurred over a two summer period. The plant had a "crowning" shape the first summer that I could not be sure was preparation for blooming, but the second summer that became clear as the plants all bloomed.
