One can get from US sailing in Portsmouth RI (401 683 0800) a publication called "PHRF handicaps". It is a spiral bound publication costing 35 bucks for USSA members (in 2002). In it you will find PHRF ratings for boats with PHRF ratings in practically all PHRF jurisdictions in the US. Assumptions as to rating include:

Max headsail 150% LP
Conventional symmetrical spinnakers
Boats set up as per their "standard class” or ex factory condition.

Since PHRF is a local arrangement each jurisdiction has particular rules that vary between areas. I have sailed on one boat that traveled and in one year we had 7 PHRF certificates to cover Narragansett Bay, Long Is. Sound, PHRF New England (Boston), Chicago, Detroit, Ft. Lauderdale and Key west race week. And they were all  slightly different….

For instance on Narragansett Bay one can get a “credit” for roller furling unit, a bigger credit if it is the only sail, more credit for smaller LP sails etc. But not on LIS.
For the C 26 the range of ratings is:
L. Erie & Mid Atlantic: 240, L. Ontario & Newfoundland  243, YRA LIS (NY) is 246 St. Lawrence Valley: 249, Nova Scotia is 250, NoCal & New England it is 252, Pac NW it is 271 Santo Domingo 308 and so on.

There is also information on the size of the data pool from each area so it is possible to figure out how many years a jurisdiction has been rating a particular class along with how many boats in the sample.The data pool for C 26 is small wirth 4 boats being the maximum, in Nova Scotia. My book is from 2002.

Cheers
Joe Cooper