What the RE told me is that you can 'crash' quickly and estrogen drops and you lose everything, so that maybe why they took you early - just a theory!
I have heard of half-doses of the trigger, but I haven't heard about taking early...even when I had OHSS, I did half-dose but they waited the typical 36 hours...
Good luck! Hope you get your BFP!
I wonder if they just wanted to make sure all of the smaller ones didn't mature any more than they had...and they were just going to use the large follicles. If they waited, there may have been too many large ones and that can be dangerous. It sounds like they did the right thing...maybe someone else will have more insight on this....someone who has been through it.