Subzonals

I recently reviewed Bill Hook's memoirs titled Hooked on Chess. While reading it I noted mention of four events that he called 'Caribbean Zonals':-

• p.066 1969 Quito, Ecuador
  
• p.080 1975 Santo Domingo, Dominican Republic
  
• p.134 1985 San Juan, Puerto Rico
  
• p.148 1990 Pinar del Rio, Cuba

The first two events square with my notes on the World Chess Championship Zonals, but the last two don't. I have:-

• 8 Caracas 1985-03
  
• 8 Cali 1990-04 • 8? Pinar del Rio CUB 1990-00

From this I gather that Hook's 1985 and 1990 events were subzonals, preliminary events where the top players in a region compete for the right to play in the zonal. I've encountered other mentions of these from time to time, but always pushed them aside, since I had enough on my plate tackling the zonals themselves. It's time to take them more seriously.

A few recent news reports mentioned that subzonal 2.3.5 was in full swing. A search on the FIDE America site returns about 19,000 from fideamerica.com for subzonal. Most of these are because the keyword 'subzonal' is currently used in a sidebar.

This leads to a few new topics of research:-

• When were subzonals introduced in the Central American zone?
  
• Are subzonals used in other FIDE zones? (I think I've seen them in Asia/Oceania)
  
• Where is it documented how different zones have split themselves into subzones?

One document which could be useful is 'Regulations for the America's Men and Women Subzonals Tournaments', but I haven't located it online.