When the media claims that the cannabis is 20x or even 30x stronger, it's just sensational propaganda. Thc can't be over 100 %, so if it was roughly 12 percent in the 60's, 10x more potent, so 10 x 12 = 120 = over 100% =/

Strains are different, some are more potent then others. I'm sure gorwers in the 60's could grow very potent strains. However, i believe with the advancing technology and strain crosses and licensed medical cannabis, it is more potent on a regular basis then it would've been in the past.