When do they typically organize the row or round robins? Do people form their own groups or do they have sign ups?

They look fun!

Last few years they were organized by a member after getting permission from admin to run them, but as so many tops went missing it appears that there are less peoPle willing to organize them. I am currently involved in both a row robin and round robin that have been organized privately, but with other board members here.
Hopefully the board run robins will go ahead again.

usually after the holidays (new year) since it is a long process that can take a year- depending on how many people in each group- and allowing enough time for each participant to add their row- and deal with the postal system
i participate in one every year- and the past couple years we have had quite a time with the shipping part- some holding up the rounds by 2-3 months due to sitting in customs somewhere - and then there is the folks who have (life happen) which causes them to be on the back burner for a time- plus with the expense involved and the economy the way it is- since it's a financial commitment too-
the one i participated in last year cost me over $500 by the end of the project- just in materials- and shipping/insurance costs.
so they are becoming a (thing of the past) maybe---
i'm not doing the international one next year that i have been part of for the past 7 years---but i am participating in a local one- a small group of friends who have decided it would be fun to do one together- we can just meet once a month and trade -no shipping involved- if someone has a crises we will know and be able to help out- i think it will be much less stressful- and definitly less expensive.