I didn't know this either, but all the reputable builders were at great pains to point this out to me.Yep, as I stated earlier ‘no amount of saving is worth the risk of lowered safety’.
It’s all a learning curve…earlier this week I had no idea that a seat with seatbelts could be put in a van without the seat having gone through rigorous safety tests.
For some strange reason the builders that used other brands of non approved seating never mentioned it.
In my experience a good converter wont assume a buyer knows it all and will bend over backwards to tell you the whys and wherefore of every aspect of the van, and they all did.