Unfortunately, Janet ... anytime you rely on mass notification to those you have not yet interacted with on a personal level, you're more or less rolling dice ... all that hard work will come down to taking a gamble (as we've even seen ... unfortunately, as a result from JVNP mailings from time to time ...).
You simply have to start building a reciprocal JV circle of partners ... one at a time, all the time ... to make sure you have a solid core of 10 to 20 partners you can rely on to push the button when it matters most.
If you are going to use JV Notification services, send out the invite a good month before launch to give you time to contact each prospective partner ... one at a time, and separate the tire kickers from the serious candidates. There is also a better chance that stronger partners will have slots open for you if you give them that advance notice.
www.ABestWeb.com offers large scale affiliate recruitment at a cost of approximately $800 a shot ... in addition to less effective, lower cost options.
Not sure if that answers any questions, Janet ... if not, please provide a little more detail.