Can known infected files be trusted if sandboxed?

[pintree3]

In the FAQ it says, "Sandboxie may be your first line of defense, but it should certainly be complemented by the more traditional anti-virus and anti-malware solutions. These solutions can let you know if your system does become infected in any way. "
Knowing the above I wonder to what degree Sandboxie could be used.
it also says, "You would be quite safe using Sandboxie. It should be noted that, from time to time, people are able to find some vulnerability in Sandboxie, an open hole through which malicious software can still infiltrate the system. "
For example, considering the 2nd point above, if I have a file for 1 or 2 months may I assume that sandboxie will have resolved the problem by then?
Also, let us assume that I have an executable file which is in all likelihood infected, by Trojan, virus, malware whatever.. Can this file be run sandboxied nevertheless and, in doing so, would this file be automatically safe from creating any infection? if yes, to what degree, 75%, 80% 99% or...?

Thanks