31 years' service confusion

NIK   Mon Jun 11, 2007 6:30 am GMT
the two policemen, who have a total of 31 years' service between them
Does this sentence mean that the two policemen's years of service are different with a gap of 30 years' time? Or does it mean that the two police have a sum of 31 years' service altogether?
Uriel   Mon Jun 11, 2007 6:33 am GMT
The sum.