It depends on what your prior surgery was. If the doctor previously resected tissue at the L5-S1 level, and now there is tissue there, then it is most likely new (or progressed). A decision regarding what is important on the MRI should be determined based upon your symptoms. If the new symptoms were in the L5-S1 distribution then I would guess that this is new. An EMG (muscle and nerve test) can sometimes help sort out what is new or old. Good luck.
I have had old injuries ( onset in 2001) to lumbar area with centrally herniated discs at L4-L5 and L5-S1. I have recently began having deep aching pain to both arms from my neck all the way to the first three fingers of each hand that switches from one arm to the other arm and occasionally affects both arms simultaneously. I am wondering if this, too, is herniated discs in my neck and if my previous injuries could have led to the onset of the new herniated discs. I read somewhere that injury to any disc can lead to degeneration of other discs as well. Is this true?