I have various Kodak and Fuji movie stocks - mostly expired -and speed loss varies amazingly. I have some Fuji Reala 500D which seems to have fallen to about ISO 80; I have much older EXR 200T that is almost as good as new. Maybe your film wasn't stored optimally all its life. But you won't know until you process in ECN-2. I use a slightly adjusted version of the ECN-2 developer that uses 5.2g/L CD3 - I have found (by trial and error) that home processing in a plastic tank, the official formula always produced somewhat thin negatives.