I have to admit, I read the thread only to page 12 and can't resist any longer to comment.
After 6 years after the OP, I still didn't know. I'm 46 right now and won't qualify for 'the oldest'.
I have two grease guns, a two-hand lever action and a pneumatic. I agree on the priming issue a poster mentioned somewhere.
Recently I bought three cheap cartridges of grease and two of them have air pockets locked in. They were a PITA. I never buy them again.
One of the tip started to leak grease out to the side. Depending which gun wasn't affected by the bad cartridges and worked, I changed the tips.
I put a new grease tip on the Financial Minister's shopping list.
When she and the kids came home, they mentioned a difference of three jaws vs four jaws. I didn't know the difference, I wasn't old enough yet.
Now, the new tip IS tight and difficult to get off some zerks.
What I discovered in the past with the side leaking is, that not always pushing the tip on to the zerks and hold it there is the solution. Sometimes I had to release the forward pressure and let the jaws hug the zerks and it would seal and not leak.
By the time I get home I will start my research to confirm your reports. If it proofs to be true, I make sure to tell my 15 year old son about it. He should not life another 30 or even 60 years until he learns this.
I really like this forum and enjoy reading on here. I apreciate the willingness of the experienced members to share their knowledge..... including a nice portion of humor about (their) "density".