I think that's normally correct, but I know of one exception from other posts here: if someone's BAEC account is hacked, in some cases BAEC seems to regard the account as so corrupted that the best thing is to give the victim a new BAEC number and new login, then eventually any Avios, vouchers, Tier Points and Lifetime Tier Points gets carried over. It's very much the exception and my impression was that BA security would deem the customer not able to keep their password secure, hence to take them out of the hackers' embrace they would issue a new BAEC number.