What is 'DOC' in terms for Depth of Discharge for SLA batteries?
DOC looks like an erroneous contraction of DOD and SOC ...
DoD = Depth of Discharge
SoC = State of Charge  

SoC is equal to 100% when the DoD is 0%, and 0% when the DoD is 100%

Regarding exceeding the 100%:


  It is sometimes possible for a battery DoD to exceed 100%, if the nominal energy capacity was estimated conservatively, or because of actual operating conditions different from the nominal operating conditions.
  Source


(the latter already suggested by @G36).