I think what might be throwing you off there is that your saves are taking on the surname of the family being actively played at the time. But in reality, the current data all of the sims in your ongoing game are in one game save, the most recent one. The data does not ever cross over between different game saves. The only point of holding onto any older saves would be to load up things as they all existed a long time ago (on purpose I mean, not by accident) or replay something that has since gone horribly wrong -- as in whoops, okay let's go back a week or two and try that again.
The game also makes one backup save for us each time Save or Save As is used and the file name is not changed since the last time. It is not necessary to save any of these much older game save files once time has marched on, unless you want a few for possible nostalgia purposes.
I have easily over 100 saves of my current (and only) ongoing nine year old game saved elsewhere on my computer and other places for backups. That's a bit overkill admittedly, but the point is that I could never lose the entire game all at once unless something really unusual and catastrophic happened. Within the actual Save folder, around five or ten instances of the same ongoing game are plenty, depending on how long it's been since I've cleaned up more or less redundant saves that are no longer required.
The households you see in the household bin by way of Edit Town correspond to Library folder files. Those would exist in any ongoing game that uses the same user and Library folder until such time as you may choose to delete them.