Okay, I found the answer to my question.
Yes, some car manufacturers have limits to the top tether.
However- there has been no known cases of the top tether ever failing on a child restraint that is a five point harness, higher weight limit seat, that is tethered. And many of these seats REQUIRE top tether use even after 40 lbs of course.
So the general concensus, is that one should go ahead and tether. Because it can significantly reduce the head excursion and prevent serious injury. Even if that top tether should fail, it has already done its job.. the childs head will have moved less upon impact before the tether gives out.
So, Tether!!!!
She and I were happy we were both kind of right : )
"Tether Anchors: Again, there is no agreement between vehicle and child safety seat manufacturers as to the weight limit for tether anchors. Certain vehicle manufacturers have stated a tether anchor weight limit; to find out check you vehicle owner's manual. In cases where the vehicle owner's manual does not specify a maximum tether weight limit, assume the upper limit is 40 pounds.
Following this 40 pound limit is very problematic, though, since many child safety seats sold specifically for children over 40 pounds REQUIRE the use of a tether. Many in the child passenger safety field believe that the risks of NOT using the tether FAR OUTWEIGH the risks of the tether not holding in a crash. Many of us would recommend using the tether no matter how much the child weighs.
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