I've seen a few threads and it seems to vary.

The bakery I work at uses a german buttercream base, like white chocolate and pure salted butter.  It tastes delicious and a lot like SMBC.  They made an extra cake and didn't sell it within a week.  I took it home for a friend to use at the end of this week.

The cake is yellow (mix) and filled and fully covered with the BC for about two weeks now.  It was frozen for over a week and currently refrigerated.  Now the party has been rescheduled for another week and I'm not feeling comfortable about using it anymore...

What is the longest it could last and be safe to eat?

-Thanks

It's probably safe to eat, but it's definitely not fresh anymore. Once you've frozen it and it's defrosted than sat around for another week I wouldn't dare have it represent my quality.

Also you answered your own question when you said you weren't comfortable. Follow your own intuitions.

A

Can you use glycerin in cakes to give them extra time

Yeah, my gut says this week is cutting it close but next week is a no.  Thanks!  Just saw your site - amazing!  Thank you :)

It's a freebie and now my friend is pushing her luck by asking for a second tier so I was trying to avoid more work than necessary... Oh, well

ADang, they make butter cream like that and put it over a cake mix cake? Kinda amusing.