Hopefully the manufacturer is on bottle, plus a lot number.  You can 
contact the mfr and access info on exact mfr date, often they give expiration
date info with lot.  You can then test the dyes against known dyes, to know
if they work properly (probably will!) and give it a new expiration date.

We did this with several dyes, and you can continue to retest, give a new
date on many of the dry powders.  I am supposing you could also just retest
as planned, and give a new date, if that is allowed within your rules in
clinical areas.  A real shame to throw away good dyes just because they
are old.  Good luck.

Gayle Callis