MOTM

Sorry if this is really basic but could any one please tell me if I 
need to be concerned about tarnished finishes on RoHS pcb's. The ones 
in question are about 6 months old and not soldered yet but have been 
stored in airtight bags. I do avoid touching the surfaces with my 
fingers but are they still usable? Also, even once soldered do RoHS 
pcbs become tarnished once exposed to air.
       Thanks in anticipation
                          Kerry