My post in the thread that @crookedpathfinder linked to may be of particular interest to you:
So, even traditionally simply going by this one factor does not make or break the working by itself, and Retrograde is also traditionally considered more of a minor affliction to begin with. You may find the working, if it is related to knowledge, trade, and other things of Mercury, may experience more delays and troubles before completion than what is normal, however, but with this other factors in the heavens should also be considered.
If it is not for something that Mercury rules over, then the planet that rules over it is rather to be considered.