Seat is outgrown sooner than advertised

We bought this seat to match the Linear Freeway pram we bought for our eldest grandson after his other pushchair broke. The pram is lovely but the seat only takes a 13kg baby if the baby is very heavy ie fat. Our second grandson was premature & we had to buy a seat for a 4lb 8oz baby so I trusted Silver Cross that the seat would last until the baby was heavy enough to face forwards as advertised. He is 13 months now but only 18lbs in weight. He is quite tall but is on the 9th centile for weight and 15th centile for height. The shoulder straps of this seat only have two positions not three as I thought. I got the cover off only to discover that I needed a Stanley knife to cut a hole in the polystyrene and cover to use the highest slots. Obviously this seat is made for other companies but Silver Cross only makes the cover for the lower slots. This is why the reviews are so low. Also why Silver Cross were throwing in a free car seat. People wouldn't mind so much if the seat was free. It is a nuissance having to find another seat for the baby until he is heavy enough to face forwards. I paid £115 for the Ventura seat at our local shop who have now ceased to deal with Silver Cross. They were so awkward to deal with. I shall take myself and baby to Mothercare and point out to them this problem so that other parents know. Mothercare in Taunton were so kind when we were looking at seats and showed us how to fit the seat in our Discovery even though they knew that we were buying from another shop. We did this because we wanted a cover to match the pram and they had sold out. So if you buy this seat and you are a slim person it won't last and you will have to buy another one. Also you are supposed to be able to clip the seat onto the pram chassis but this is dangerous for a baby who can't hold it's head up. So I wish I had bought a Britax since I have never clipped the seat onto the chassis. Finally this baby is still small enough to fit into the bassinet of the pram but he has to use it as a pushchair because he tries to climb out. So he's not that tall and the seat is still outgrown. Ok if the seat is free but not if you have to pay for it.