Basically this. HoH:MC explicitly states that the Order as a whole knows remarkably little about House Bjornaer (with most not even realizing this without someone pointing it out). That being said; Mystery Cults are gonna act like Mystery Cults; that alone ought to make Bonisagi relatively familiar with the concept to make them pause.
Secrecy and mystery are their source of power - apprentice snatching could compromise those; and since Bjornaer have a whole Clan dedicated to silencing anyone who would steal House secrets, I doubt there'd be any misconception about how they might respond to Apprentice-snatching. Conversely, if the Clan operates more covertly, the Bjornaer-apprentice track record should at least give the Bonisagi some ... concerns.
Alternatively, just look at how Verditius reacted to someone leaking their secrets. Criamon probably wouldn't be too bothered, their secrets guard themselves...Not sure about Merinita.
In general, I don't see bonisnatching happening often, but it could well happen, and for various reasons.
It could be from wanting that spectacular apprentice for himself, to 'save' the apprentice from a cruel/tormenting master, to assert dominance over a rival, or even out of a petty reason "I can, therefore, I will".
The reason, or even the perceived reason by the former master, will dictate how, if any, reaction, this will get, and could well affect the story.
Maybe I am being misdirected by the fact the average parens can effectively choose any apprentice Gauntlet, and that the Order as a whole ignored the Merinita civil war in the early as "in House" business.
As such I was under the impression that House Bjornaer had made the Order accept that anyone initiated into Heartbeast was a full mage - though the ex-Apprentice does get the rest of the 15 years of training
The Order does not accept anyone as a full mage and member of the Order until they have sworn the Oath of Hermes, and Bjornaer apprentices generally don't get to swear that until they have had the customary 15 years of training.
See HoH:MC p16
House Bjornaer does not, in general, tell the rest of the Order anything at all about how Bjornaer operates internally, which includes how they train and treat apprentices. They won't bother making anyone else accept how they do things - they will just do it anyway and not tell anybody about it.
If you take an apprentice with a heart beast there is going to be trouble- bjornaer already consider them part of the house
Now assuming bjoraer are proud of their apprentices heart beats people will be somewhat familiar with who has them and who doesn't, and the fact that about every12 years a whole bunch (relatively speaking) of bjornaer apprentices will have heart beasts
This awareness is more likely for any Bonisagus who contemplates Bonisnatching and wants to avoid problems. It doesn't require access to their inner mysteries to make these observations.
I would say that a regular gathering of an entire House would be something other magi are aware of. So the Twelve Year Gathering, and the Verditius competition would be known events, even if the details might not be.
Sort of.
I play the Gifted son of a player maga who always wanted to train him herself but was slow to develop the required arts. One of the beta-SG ran a story where a bully of House Flambeau turned up to claim the boy who had gone years with the manifest Gift and no arts opened. Fair and square.
It ended with the beta-SG's own player magus, a follower of Bonisagus, promising that he would come and claim the boy once his arts be opened. The Flambeau thought twice about the matter and left without the boy, who started training with his mother a few years later.
This story would have been a lot more fun if the Flambeau had become a recurrent bully, but a decade has passed without hearing more of the matter in game.