ROTH conversion at Vanguard and 1099-R fields

[esarnc]

I am trying to assess potential 2023 tax implications for Roth conversions using 2022 TT (I understand the tax brackets limits will be different but this is for pure planning purposes). I have two IRA accounts with Vanguard, one has funds rolled over from my previous employer's 401K plan and the other has a non deductible traditional IRA  contribution account. I am over 60 years old. I plan to do a partial conversion and am wondering how (what field values) will the 1099-R form that Vanguard issues in 2023 looks like. 
The customer rep I spoke to at Vanguard was helpful but clueless. 

Here is my assumption using $1000 as a converted amount.

Box 1 $1000
Box 2a $1000
Box 2b Not checked
Box 7 1st code is 7
Box 7 2nd code empty
Box 7 IRA/SEP/SIMPLE checked

Vanguard rep mentioned that
(1) Box 2b will not be checked because from Vanguard perspective the whole distribution is taxable and I need to  keep track of the prorata values myself.
(2) Not sure if the Box 7 IRA/SEP/SIMPLE will be checked. 

If anyone has done a Vanguard ROTH conversion  in the past and has a 1099-R, appreciate your feedback on my assumption on 1099-R fields.

[dmertz · Accepted solution]

The Vanguard rep had it backwards about box 2b or you misunderstood what you were told.  Box 2b Taxable amount not determined is required to be marked on any Form 1099-R with code 7 in box 7 for a distribution from an IRA for exactly the reason that the Vanguard rep said, that determining the actual taxable amount is done on your tax return, not by Vanguard.  The IRA/SEP/SIMPLE box must also be marked.  The Vanguard system will automatically mark this.

All of your traditional IRA accounts are treated as a single IRA account for the purpose of determining the taxable amount of a Roth conversion.  The calculation is done on Form 8606.

[esarnc]

Thank you @dmertz . I will heck again with Vanguard on box 2. 

[dmertz]

Front-line reps rarely understand how Forms 1099-R will be prepared.  Instead, see the instructions for Form 1099-R:  https://www.irs.gov/pub/irs-pdf/i1099r.pdf