Your question spiked my curiosity, so I checked on Fiocchi's website for the answer. As it turns out, only the #616 primer is listed. It is described as "209 size," so I'm GUESSING that the #617 was a different size and may no longer be made.
The 617 is a relatively new product and is reported to be hotter than the 616...more like a Fed 209A. Ballistics Products is selling 12 ga. 3½" primed Fiocchi hulls that contain the 617 primer and BP describes them as a "magnum" primer.
Check with Hodgdon and Alliant, since it appears they have done some testing. Check with Fiocchi also, since they manufacture them, There was a #615, which was slightly over sized and the the #616. The #617 has shown up in some areas and is supposed to be a new primer. No quessing about loading data. Get it from the source, powder or primer.