This isn’t quite right. The Jewish community institutions have been well aware of IHRA for ages as there was a big debate over the government adopting it (including a very well publicised home affairs select committee inquiry in 2016
You can read the oral evidence from that inquiry where eg the chief rabbi directly addressed the definition data.parliament.uk/writtenevidenc… 
But Michael is right that *many* Jewish people were probably not aware of the IHRA definition before this summer. I admit I was vaguely aware of it but hadn’t read it carefully and hadn’t been a strong advocate either for adopting or not adopting it (as far as I remember)
The danger as with any hard, emotive debate is you become attached to things like the definition because it’s what *your side* want & lose sight of the true value of it. I think I have been clear that I am not a *huge fan* but think there are good reasons for Labour adopting it
