Great question. There's lots of variables to this schedule conflict.
I can tell you that when I was RaceChair of one of the eastern clubs (EMRA), it was real hard to get dates unless you asked 3 or 4 years ahead of time.....and even then, with no guarantee.
That's essentially what Marianne Shoemaker (at Watkins Glen) told me.
Each track has it's own system and date calendar and there's really no coordination between them (unless the clubs facilitate it).
Also, there at least two new tracks scheduled to open and we already have two fairly new ones in the northeast (plus the effects of the "club thing" at Lime Rock). So things are likely to get more complicated.
I know that me and others at VRG have been urging Tim and the guys that run the Classic Motorsports Small Bore Cup to move their Savannah date so they could also join us at our Jefferson 500 event. We've finally been able set this up for 2011 (and are very happy), but this stuff takes time and there always seems to be a mulititude of factors affecting things.
A few years ago, NASCAR wanted a last-minute, extra weekend of testing at Pocono. So they "bumped" the NASA-NE region out of their slot (at the last minute). Since NASA-NE had more dates at Pocono, the managment let them bump EMRA out of a following weekend. This stuff happens regularly between the bigger for-profit groups and smaller, non-profit clubs. And it's not always done nicely.
VRG has been running a growing, early September vintage event at NJMP for the last three years. This year, SVRA has walked in and has taken that event over. They have more money and have paid staff to push their viewpoint. I guess that's the way it is.
By the way, it'll be interesting to see how things go at SVRA. Peter McLauglin in now sole owner (as of a few weeks ago). In the past he was part-owner and SVRA and HSR had a partnership. HSR has now been divorced from SVRA. And Carl Jensen (the guy running SVRA on a day-to-day basis for a number of years) has suddenly left. And there's Rahal's group, which looks like a flop, but may still compete with SVRA somewhat (it'll have no real affect on the smaller clubs). Lots of stuff happening that makes future calendars seem hard to predict.
Meanwhile, some of the smaller, non-profit clubs are trying to work cooperatively. VRG has VDCA and VARAC on their calendar (and vis-versa). You may see more of the small clubs banding together to survive.