I'm not sure what the default configuration of a 228 cab is but I'm pretty sure it doesn't support 288 ports from the outset.
They don't; They start with only 1 or 2 line cards (To my knowledge) and then when the software which keeps track of customers on a cabinet senses a take-up percentage of more than 75% (I believe this is the figure), it triggers the order for more line card(s) to be installed by Openreach.
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A.K.A: Chrisszzyy
Telewest (2004-2006): 256Kbps -> 512Kbps
University of Portsmouth's Horrible Network (2013 - 2014) - Supposedly 100/100Mbps
BT (2006 - Present): 8128/448 -> 22494/1211 -> 79987/20000Kbps (BT Infinity 2 on Huawei Cab)