401(k) In-Plan Roth rollover (IRR) vs. In-Plan Roth Transfer (IRT)

Can someone shed light on the difference between IRR and IRT?  Our BPD Cycle 3 says IRR involves an amount "permitted to be distributed in an eligible rollover distribution" and IRT involves an amount "not otherwise distributable."

An IRR I believe allows in-plan conversion of pretax deferrals at any age.    Beyond that, I'm not 100% and can't seem to find sources that explain this well.

We were to amend a plan to allow in-plan conversion - presumably both IRR and IRT.  Amercan Funds RKD says on their website they do not support IRTs. 

Thank you for your comments.

22 minutes ago, Tom said:

IRR involves an amount "permitted to be distributed in an eligible rollover distribution"

This means amounts that could be distributed from the plan. For example, 401(k) deferrals if the participant is over age 59½. There are other distributable events for 401(k) deferrals, of course, but those would not generally be of much use in an IRR context. Terminated employees can't usually make rollover contributions, and hardship distributions aren't eligible rollover distributions, for a couple of examples.

24 minutes ago, Tom said:

IRT involves an amount "not otherwise distributable."

This is anything that couldn't be distributed from the plan, for example 401(k) deferrals or safe harbor contributions under age 59½ while still employed.

25 minutes ago, Tom said:

Amercan Funds RKD says on their website they do not support IRTs. 

If a plan allows a Roth conversion of amounts that are not otherwise distributable, then it has to retain the distribution restrictions that applied to the amounts prior to the conversion. That means, in most cases, the plan will have to track twice the number of sources that they had in the plan before. For example, now they have 401(k), 401(k) Roth conversion, safe harbor, safe harbor Roth conversion, profit sharing, profit sharing Roth conversion, etc. That might be the reason why a particular platform isn't supporting this type of conversion.