IMHO itīs an interesting question, because there are different reasons. So The Marvelettes had no high voices after Georganna and Juanita left and the group uses The Andantes. On the other hand Martha & The Vandellas uses The Andantes after her Dance Party album totally, often without The Vandellas, together with Ashford and Simpson or Syretta Wright. IMHO it looks like a solo singer named Martha Reeves, with backround voices The Vandellas, sadly we have not enough live material of MR&TVīs to have an opposite, the only very good live performance of the Group is "At the Copa" and thatīs not released until yet. For me personally The Marvelettes are a group from the beginning to the end. And "The Return of TM" was an open secret with the talented Wanda Young. We have a lot MR albums, which contains no or less Vandellas like "Sugar`n`spice", "Natural rescources" or "Black Magic"
What you are think about that fact ?