Repeat SNB

I've recently been diagnosed with local recurrence 9mm (primary was in 2000) and am scheduled for bilateral mastectomy.  In 2000, I had 3 sentinels plus 11 other nodes removed - all negative, but not sure if this was actually a complete dissection or not.  With the recurrence, I've had CT with and without contrast as well as PET/CT scans and neither shows any axillary involvement.  Is it possible or recommended to do a SNB again?  Someone recently suggested scintimammogram.  Would this help in any way?  Thank you!

[Cleveland Clinic]

Dear gadabout:  Your initial lymph node removal would not be a complete axillary dissection but, rather, a sampling of lymph nodes or partial axillary node dissection.  Nonetheless, in the setting of a local recurrence, it is often not feasible to go back in and take additional lymph nodes.  

[gadabout]

Can you elaborate a little on why this is "often not feasible"?  I didn't mention previously, but I have had whole breast radiation which I have heard can make repeat SNB not accurate.  But doesn't the lymph fluid somehow redirect, so could there be another sentinel node now?