score:4
Applying should be OK, if there is no overlap between the visas. Otherwise, you can go to a consulate from the country that issued the first visa and have it cancelled before applying for a new one.
What is definitely not OK (and perhaps the source of the confusion you found on the web) is having two visas with overlapping validity. Thus, if you had to enter on August 1 and stay later than August 9, the second visa could only be valid from August 10 (see this earlier question for an example).
The main source of official information about all that is the EU's pages about Schengen and in particular the Handbook for the processing of visa applications and the modification of issued visas. (EDIT FOLLOWING COMMENTS:) This particular issue is dealt with on page 26:
A holder of a multiple-entry visa may apply for a new visa before the expiry of the validity of the visa currently held. However, the validity of the new visa must complement the current visa, i.e. a person cannot hold two uniform visas valid for the same period in time.