>>> So the DSLAM's either have different versions of line cards in them or they have the same line cards with different firmware on the line cards.
They certainly do use 2 different types of line card on the ECI's. I tried to do some digging into this many years ago.
Bearing in mind we are going back probably 8 years, my memory is hazy... ECI manufactured 2 different 64 port vdsl2 linecards. The newer of which were specifically designed to work with the V41 (Vectored) MSANS but are backwards compatible and also work in the M41's.
What Openreach call in some of their documentation the VTU-C64P V3 card contains the Lantiq Vinax V3 chipset. The older VTU-C64 contains a Lantiq Vinax 2.2 chip.
FYI my stats identifies as IFTN:0xb206 (178.6) / v0xb206
From a photo taken inside my DSLAM I can see there's a bar code & sticky label on the linecard which says VTU-C64P
Both versions may be embossed with VTU-C64 so its not possible to tell from normal photos which is which and I'm not sure how significant the 'P' is when it comes to identification. There are other numbers on the sticky label but they relate to 'BT' and a Serial No