First Year of Roth

Can anyone explain why IRA custodians request the "first year of Roth" when a Roth 401(k) is rolled over to a Roth IRA?  The 5-year clock starts over when Roth funds are rolled over from a 401(k) to a Roth IRA.  Besides the fact that I also don't understand WHY the clock starts over, why is this data collected?

18 hours ago, Brenda Wren said:

why IRA custodians request the "first year of Roth" when a Roth 401(k) is rolled over to a Roth IRA?

You're correct that the Roth clock starts over. I received a check for a Roth 401k rollover to an IRA and it stated the date of the first Roth contribution in the 401k. I wasn't sure why it was on there either. I don't see any reason why the receiving custodian would need to receive that information. 

I have not looked at this lately so I could be completely off base here.  I thought when you roll a Roth 401(k) into a Roth IRA, the holding period of the Roth IRA determines whether the 5-year rule has been met.  So, if you roll an old and cold Roth 401k into a new Roth IRA that you open up to receive the rollover (and you have no other Roth IRAs), the 5-year holding period restarts because the Roth 401k holding period is irrelevant.  However, if you roll the same old and cold Roth 401k into a Roth IRA that you first contributed $1 to 6 years ago (and nothing since), the holding period would be based on the Roth IRA and thus the 5-year holding period would be met.  (I thought there's a rule about aggregating all your Roth IRAs and using the oldest holding period but that might not apply in this instance (since there are so many five-year holding rules).)   I guess I was wondering when they ask about the first year of Roth, are they asking about the 401k or the IRA account(s)? 

Sorry if I am completely off base here.