Penalties under SA for Carelessness

Dear All

does anyone have experience with tribunals view on careless behaviour by clients on SA returns

our client checked some of their tax return but did not check which remittance basis charge box was ticked under the new regime in 2015-16, giving rise the wrong rbc being levied, as the incorrect date of entry to the uk was entered onto the tax return system by ourselves

our and the client view is that they acted reasonably by reviewing all the numbers ie income and allowances but as we did not point out the importance of the date under the new regime did not consider same

the penalty hinges therefore on what is careless behaviour

if anyone has experience of penalty appeals or relevant cases please advise

thank you