I hope your dog is ok and I wouldn't now take anything for granted, but I use to feed my first lab hundreds at a time off the vine at home (before I knew they are toxic). She lived to be 14 years old. If its been a couple of days and your dog hasn't had any problems yet your probably ok.
Wouldn't panic. My first lab loved them as treats. Funny thing, he wouldn't eat them at first. I had to squish one so he could taste it first then, after that, he knew that he had to CHEW them to get the goody. Never fed more than a few at a time, and was before anyone said they could be a problem, but he lived to be 15 and never had a problem with them (suppose he might have lived to be 20 if I hadn't been feeding him an occasional grape, bit of chocolate, and let him lick the guacamole bowl). Second lab got all of that stuff too until we began to hear what might be toxic, never seemed to give him a problem either. Mostly withholding from current knucklehead, but does get to lick guacamole bowl now and then (after I have had a good go at it first).
Um...my 62lb 6 year old female counter serfed herself to somewhere between 25-30 grapes while we were at the movies last Sunday. Didn't eat the bag or stems...the picky eater! Came home 3 hrs later and immediately gave her hydogen peroxide with no luck....she wound up at the emergency overnight for a charcoal treatment and 48 hr IV drip as recommended by animal poison control. She's home now and appears to have weathered the storm. Those were some expensive grapes! Supposedly the toxicity of grapes is not well understood. One grape is too much for some dogs while others can process one per pound or pound and a half of body weight.