Returns rate statistics, education breakdown, business size breakdown,
and labor_categories for a GSA MAS Special Item Number: the 25 titles
with the most rates on the SIN, with counts (exact, case-sensitive
titles). It does not return individual rate rows or per-title prices;
for what a title costs on the SIN, call igce_benchmark(title, sin=...).
When GSA's 500-title list is cut off, labor_categories.distinct is null
and records_in_titles_not_listed counts the rates under titles not
listed.

Common SINs for professional services (live-verified to return records):
- 54151S: IT Professional Services
- 541611: Management and Financial Consulting
- 541715: Engineering R&D
- 541330ENG: Engineering Services
- 561210FAC: Facilities Maintenance and Management
- 611430: Training