This is an interesting bit of information. It would make choosing seeds a little easier in future.
I will offer this though...in the Marijuana Growers Bible it states that sex can be set during the growing stage through temperature management alone. I have grown several plants from seed, without checking for the depressions, and by maintaining the optimal temperature to grow females, have only ever had one male plant in my stable.
If my memory serves, since I don't have my bible handy, females are more assured when the temp is consistently between 72-76 deg F. I am sure there are more qualified members here who can either verify this or not, but I have had extremely good success with this method in producing females.
For those of you buying seeds this may be a trick to try with those seeds that are identifying as male in seed form.
Stay loose all,
79stingray