Reply #2: Normally in this type of case

[Yupster]

it would go to arbitration.

Brokerage firms carry "Errors and Omissions" Insurance to coiver situations like this where the broker or company failed to due a trade due to an error or omission.

Generally each person gets a statement at least quarterly, sometimes monthly. The investor would be expected to explain why it took him ten months to notice the omission.

I don't know if the account being a 401 (k) makes the process significantly different from a normal brokerage account.