The servicing stickers are no more than the same kind of sticker your child gets when visiting the doctor and getting their inoculations done ! They have no legal significance whatsoever.
The only record you are advised to keep up to date with is the stamps in your service book and the receipts from the workshop doing the servicing.
The only people who take some, but not a lot, of notice are the Police and VOSA when they stop you as the sticker gives a first glance idea that the van is at least roadworthy and the owner does take pride in their outfit.
As for the rumours about sites demanding various certificates for gas and electric that is simply not true, it was mooted by the AWS and was seen as a money making ploy, even the main clubs distanced themselves from that rumour.
As engineers we were forced to go on expensive courses for 230vand 12v system testing and certification, then promote the myth of sites needing said certificates.
I will not go over it all again as it was a disgusting ruse and I firmly believe that for someone not already familiar with electrics, a two day "course", most of which had NOTHING to do with caravans, was enough to "qualify" the engineer.
Myself, and some other engineers I know, even though being 17th Edition certified was not enough for the AWS, we still had to go on these stupid "courses" at over £600 each.