IF no QDRO is ordered at the time the divorce is granted, can one ex spouse go back 3 years later to try and get a dispersment from the other ex ?

Yes!  QDROs Qualified Domestic Relations Orders) can be entered at any time to provide for direct payment to you of your share of your ex-spouse's retirement benefits, assuming that you were granted your marital share in the divorce order. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.