State Retirement Pension - WASPI - Backdating voluntary Class 2 Self-employment NIC beyond 6 years

Would be grateful for any advice on the following including any potential pitfalls for client?

Client’s retirement age is 2024, although she had been registered for tax since as a self-employed person since the 1990’s, she did not register her self employment for class 2 NIC’s until last year.

HRMC have agreed to her paying backdated class 2 voluntary self-employment NIC’s for the past 6 years (£3 a week for 2019/20 rates).

But not beyond that period i.e. she would have to pay class 3 voluntary to 2005 (£15 a week 2019/20 rates).

HRMC have accepted her her failure to register before last year was from ‘ignorance and error’, but that her ‘error’ was ‘due to a failure to exercise ‘due care and diligence’.

Citing the following

1. she did not register with the DSS when she became self-employed in the early 1990’s.
2. it remained her responsibility to notify the relevant agencies that she was self-employed and needed to pay class NIC’s.
3. When she registered for income Tax the Inland Revenue would have sent returns and notes which explained that self-employed people are generally liable for flat rate Class 2 contributions, details on contact NIC office for further info on registering for Class 2 NIC’s. But she did not act on these.
4. Finally, she could have made enquiries with HMRC or it’s predecessors about paying Class 2 NIC’s before 2020.