Closed Tab Groups can't be found

I had multiple tab groups which I had chosen to save and close. These tab groups have now completely disappeared and I cannot find them. When I began using Tab Groups, I had checked and there was no information stating that unopened tab groups would be deleted. I want these groups back. If I had known Tab Groups would disappear, I would have saved my tabs into a folder. The only Tab Groups that show up now are under "Recent tab groups". If tab groups are going to be deleted after a set period of time, it should be stated clearly in the tab group settings. It would also be really useful to archive them into a bookmarked folder so people don't unexpectedly lose hours of research.