> Terminology: in the tax preparation industry, "pre-tax" and "post-tax" usually only refer to contributions (not account types) that are or are not (respectively) excluded from current income. Earnings in the account over time are either tax-free or tax-deferred (depends on account type and what the distributions of said earnings are eventually used for), and distributions are either taxable (possibly with penalty), or tax-free.

This is all true as far as it goes. However, if you've ever had to do any work for one of the trust custodians, you'd be keenly aware that DOL regulations require that all the different types of contributions be segregated into different accounts - or if you physically commingle the funds, you have to account for them separately on your own books.

So there are in fact different accounts for pre-tax & post-tax... except it's actually more like pre-tax employee contribution, pre-tax employer match, pre-tax employer profit-sharing, post-tax employee contribution, post-tax excess contribution, etc. etc.

These different account types are used to track the tax character of the eventual distributions. If you didn't have different pre- and post-tax accounts, it would be a frickin' nightmare to prepare forms 1099-R