Guide 62 also states how to determine how many sites to sample based on the total number of facilities. I can't recall the formula, but it is basically a fraction of the total number of sites. The auditor days per site is determined based on a table of number of employees.
Registrars do have some discretion in how they quote. If you have five office employees and 200 truck drivers, they do not have to quote at the 205 count. They can also reduce the time if you don't do design, or increase it if you have a complicated/multiple scopes.
I also get creative on what I tell the registrar. For example, 2 part time employees = 1 full time. I will do this to meet a breakpoint in the chart if we can - usually in the 10-15 person range.
Tom