What happens if we use expired tissue culture flasks (T-162 Flasks) for vero cel - (Jul/29/2013 )

One of my QC technician used expired t-162 flasks for vero cell passage. The cells were looking fine and there was no contamination.

Can any one suggest me how to provide justification.

The expiry is usually for guaranteed sterility, so most of the time this shouldn't be a problem, so long as the packaging is intact.  Some culture vessels have substances (e.g. gelatin) added that can degrade with time, I wouldn't use that sort past expiry dates.