Hey even though you aren't hitting the weights you would like to on this given day, you are making huge improvements. Look back at your 6/12/12 video and compare to these most recent ones. Your turnover is WAY better, you are able to get those elbows up and around better than before. Your rack position and jerk rack position are improved also. In this latest video you are able to support that weight on the shoulder.
For the jerk in 70kg and 80kg, you are having some trouble in the dip and drive that is leaving that bar out forward and you aren't able to get a full drive into the bar. Part of the problem is that you are dipping a little to far and by going to far down you are beginning to squat instead of dip and drive. That squatting position is tilting you forward and also causing some problems finishing the drive.
To remedy this I would suggest some jerk dip squats where you focus on keeping that dip and drive straight and with slightly less depth. Another exercise that will help would be a pause jerk, where you hold the bottom of the dip and really focus on driving straight over the neck. Before you initiate your jerk I would suggest pulling the face back to get it out of the way and to remind you to drive the bar straight up. (This video has some pause jerks in it: http://www.catalystathletics.com/med...hp?videoID=274
For the pause jerks make sure you keep those shoulders up (to keep the bar from pinching your artery) and stay conscious as they will sit on you and make you feel like you are about to pass out so take caution!
Overall I can see you are making improvements so I would say to stick with the stretching and mobility work and keep working at it. Part of adjusting your mobility will be gaining strength in the new positions as they improve, it will always be a process but the pay out is rewarding.