Gunmaking in Europe, especially the major centers of production, was very different from working processes here.
There were pattern books and makers in different shops, towns and even countires used patterns or adapted patterns from these books. For most of the flint period then artistic center of firearms decoration in Europe was Paris and the innovation in design tended to flow outward from there. Pattern books were just one way it moved from city to city. Frenchmen fleeing religious persecution in their home country by moving to England gave their new country quite a boost design wise.
Going back to your particular question about Jaegers---the carver was often a different man from the stocker, the mount making could be several different trades as well, the engraver could be down the street, etc. So attributing a rifle to a particular shop based on carving or engraving alone would not be very reliable. The exception being that execution of micro details in the same design might lead to a particular carver even if it is a design from a pattern book.
So when someone says your can make an attribution or at least an association based on the carving on two longrifles they are usually on solid ground (not the attribution itself but the statement that one could be made
. I say usually because there are examples in longrifles of journeymen carving rifles in a style different from the style of the master they were working for at the time.
Gary