your ovaries won't recognise whether one or three embryos have implanted - the HCG was recognised and the corpus luteum were created.

i would take notice more of the pre-ovulation information regarding mature follicles than the post ovulation CL size. follicular development is very standard - 1-2mm per day, and has to be a certain size for a mature egg to be released - if there was only one follicle large enough when they triggered, there would be no way others could increase to maturation rapidly (trigger stops growth of follicles).

as i mentioned, i used to get upwards of 20 immature follicles and between one and three dominant follicles during an IUI cycle - the cycle my daughter was conceived, i had one dominant follicle but well over 20 immature follicles on my right ovary. at the early scans i had, my ovaries were described as chunky and covered in corpus luteum from the immature follicles...