Yes...things may be different b/t the two tests. Always check the alt on these new, more electronic cars, first. Like someone said here before...a faulty v reg. will screw up many of the other systems with its variable spikes or low output.
I'm finding in the two newer MBs I've owned and driven over 100,000 miles that the v reg. and alt seem to need replacing regardless of how well the car is maintained and do cause other systems to show 'false' codes in the memory. Nothing worse than changing out expensive modules and parts only to find out later that only the v reg. was worn a bit.
Food for thought...though I'm only a backyard mechanic...and certainly no expert by any means.