What your situation is the 401K plan administrator probably thought you were rolling the funds from the 401K to a traditional IRA hense the code G. If you made the rollover to a traditional IRA in one tax year and then converted it in another tax year then you will report the conversion in the year of the conversion ... another 1099-R will be issued for that conversion.
However if you skipped the traditional IRA rollover and converted it to the ROTH directly then you will need to use a code 7 in the box 7 of the 1099-R and NOT the code G.
