I bought the SICT. I didn't pay so much attention to the # or the claim. It was more the fact that there WAS side impact protection, or an attempt at it. And the Advocate has head wings. Ought to be better than nothing.
BTW, if a car slams into a child I don't see any seat on the market as being all that great. Is THAT what side impact is for, or is it simply the child's body hitting something in the car?
A member here was recently in a crash. Her child was rear-facing in a MyRide. He was pretty much at the point of the impact, I believe- the car was t-boned and his door was crushed in and destroyed (he was outboard.)
The child came away with some minor bruising from the harness.
The MyRide does claim "side impact tested" though the claims are not as extravagant as some seats on the market, but I don't know that it would have fared all that well in this crash if it had been used forward-facing. The rear-facing position was able to let that nice high shell contain the body and spread the forces widely, so the child was protected as well as possible. Very importantly, mom knew how to install and use the seat properly, so the seat was tightly installed, and child was tightly secured in the seat.
To me, using any seat that seems to contain the child well, and using it rear-facing as long as possible is the best way to protect the child. Whether one product or another has one or another type of "side impact protection" probably doesn't make as much difference in this grand scheme of things, as long as, as you say, they make some effort at it, and it's used properly, and rear-facing as long as possible, then properly tethered, etc. That's the sticking point, and why I'll prefer any seat that allows the longest time rear-facing!