Pet Buckle, large dogs and LATCH

Riddle me this: I have the PetBuckles for my 80 and 60 lb dogs. They came with a LATCH strap and a seatbelt D-ring loop. I get that my car's anchors are only 40 lb anchors, so I can't use the LATCh strap connected to those.But my mom's 2007 Sentra should have the SuperLATCH and I could theoretically use those anchors for both of my dogs, right?
Why don't I need the SuperLATCH strap and connector to use the anchors in my mom's car or on the D-ring with my over 48 lb dogs?
And why did the instructions say I could use it to 40 lbs with standard LATCH when it would only be connected to ONE anchor and they are tested using BOTH anchors? I Can I extrapolate that if I can use one to 40, then I can use TWO to 80? Can I connect a car seat LATCH strap between the two anchors, and attach the PB tether to that?
Am I making sense?
They currently ride third row with seatbelt, but if I only have one dog, it would be easier to have them second row outboard. Plus my 60 lb'er steps on the buckle release button and unbuckles herself.

Vehicles don't have SuperLATCH. Only the Radian does.

The reason that you can use a SL Radian past the vehicle's weight limit is because they have tested their seat and they know how much force is placed on the anchors, and it's less than the federal minimum standard. But with a different seat (or in this case, the PB harness) the forces will be different and so you can not exceed your vehicle's weight limit.

I'm guessing that it's essentially the same reasoning for why you can use the LATCH connecter with the PB on only one anchor up to 40 pounds even though your vehicle's weight limit is 40 pounds. Regardless of what your vehicle manufacturer says the weight limit is, the anchors have to meet a minimum strength limit. The PB manufacturer must figure that it's strong enough to restrain a 40 pound dog. I wouldn't connect a strap to both anchors and use it to 80 because the anchors will not be loaded evenly except in a very precise set of circumstances which would not be realistic.

For your escape artist dog, I would either use a carseat LATCH strap attached to both anchors as a backup to the seatbelt in case she releases herself, or get something like the Angel Guard which is designed to keep children from unbuckling themselves. Neither is something I would recommend for a human child or a carseat, but dogs aren't children and PetBuckles aren't carseats.

Thank you!
I guess I'll look into the Angel Guard since I can use that whether she's in the second row or the third row (no LATCH back there).
I think I can put one in each driver's side outboard seat and they can't unbuckle. They step on the rigid buckle stalk in the center and passenger outboard seats in teh third row.