Just checked samknows to see if the 21CN date had changed. And it has to "Not Available" which is rather disappointing. IS it likely to reappear or will the the 21st century be passing me by? 
It
could just be an error in the system.
When my exchange was due to be upgraded (Only 1415 lines) the checker went all weird and started outputting strange results in the last 3 months (The due date kept advancing every day by 1 day so it appeared it would never be completed -
http://forums.thinkbroadband.com/btsupplier/t/407166... ). It did this from 1st December to 1st February; I'm not saying its the same for you but it could be a possibility.
I do recall my exchange losing the information that it may be upgraded at one point.
I wouldn't trust Samknows by the way; At the same point as the problems were occurring with the Wholesale Checker, SamKnows indicated a date of 31/03/2012 by which point I was already enjoying the speed increase.
Fingers crossed you get some good news soon.
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Downstream Upstream
Connection Speed: 22494 kbps 1211 kbps
Line Attenuation: 16.0 db 9.7 db
Noise Margin: 2.6 db 6.7 db
Telewest (2004-2006): 256Kbps -> 512Kbps
BT (2006 - Present): 8128/448Kbps on 20CN Alcatel DSLAM -> 22494/1211Kbps on 21CN Huawei MSAN