Tissue kept over 12 hrs in formalin can have real problems in IHC, but I have 
used 10 yr old blocks for controls with no problem, so I am assuming 
thatfresh cuts from old blocks do not have as much problems as over-fixed 
tissue. I have no scientific evidence to prove this, just 8 years of immuno 
work.
                                                    Dana Dittus
                                                    Histology Supervisor
                                                    Abington Memorial Hospital