Look at my article on evaluating engine controls in the DIY section. The impulse counting methods that are described apply to SRS in that model. Erasing the codes (EXCEPT CODE 10) will also follow the same rules.
If an airbag has been set off by a controller of that age the controller will have a code 10 set and have to be replaced. Later versions can be reset a given number of times (three I think).
Bosch Master, ASE Master, L1
33 years MB technician