We are talking about PHRF - right?
That's the point. There isn't an official number. It varies by local fleets. And could vary within a particular fleet depending on what sails are being used or by type of prop being used on boats with inboard engines. It can also vary due to the skill of the crew. If a particular boat is winning all the time there could be pressure to lower its rating in that fleet. And vice versa. That might not affect other local fleets. It also can vary by local weather conditions. PHRF is a performance based rating as opposed to many other rating rules which are derived from design parameters.
PHRF New England does not have a rating for an O'Day 192 (This could be outdated) which probably means no one is sailing that particular design in that local fleet. In that case if you apply for a PHRF rating the fleet handicapper would look for other fleets which have a rating for the 192. Normally they would rate an unknown boat at the lower end of the range because it's easier to give time than it is to take time away.
PHRF ratings assume that your boat is in racing condition and the crew is skilled. If someone comes out un-prepared in any way, dirty bottom, extra weight on board, crappy sails, don't have a copy of the sailing instructions or are known to sail poorly, requests for time won't be successful.