Is it necessary to identify verses and choruses in vocal songs when there are no corresponding identifiers in print? If so, is it also necessary to identify them in a piano accompaniment? Or is it sufficient to insert measure numbers into the vocal part without specifically identifying them as Verse, Chorus, Bridge, etc.?
Your answer depends on the individual piece. For a through-composed piece - one with no repeats, I think measure numbers would suffice if the verses are not specifically labeled as such.
However, if you are transcribing the music for only the first verse of a strophic song and then brailling only the text for the remaining verses, you must list verse numbers, as seen in example 35.7-1 in the MBC2015.
If the refrain is obvious and a part of the repeated music that is not brailled in full the second/third time around, you would label it as such, even if the label is not shown in print. (Ex. 35.7.2-1)
Those added labels help the reader orient themselves when there are repeated portions of music that we are not transcribing in full.