I settled in 2014, and also received the loan charge letter last week.
I took a close look at the CLSO 01 wording:
You can settle your affairs now. This will give you certainty about your tax liabilities and save you and us costs.Reaching agreement now will mean that liabilities in relation to sums you have received under these arrangements of years up to and including 2010/11 are final.
Looks unambiguous. But the next line says:
During this settlement opportunity we will restrict settlement to 2010/11, and earlier years for which we have open enquiries or assessments. If any future proceedings we will consider the conditions for all potential years of charge to 2010/11.
So the key question is whether HMRC had an open enquiry for all years up to 2010/11, or only some. I've contacted HMRC for clarification via email (I couldn't get though on the phone) so will have to wait and see.