Interesting info. And yes, the film I'm referring to is "Velvia", not the newer Velvia 50 which according to what I've read, has "improved" reciprocity characteristics (not sure what the improvements are though exactly...)
I shot one roll of it so far using my Holga, just for fun and to see if the film was still any good. I expected most of the shots to come out underexposed, considering the shutter speed is around 1/100th and the aperture is around f/8, which seems like a pretty short exposure in most lighting conditions for a 50 ISO film. When I picked up the chromes, I was surprised to see that pretty much all the frames came out, underexposed, but still not too terrible. I made a couple nighttime bulb exposures just guessing at the shutter speed (around 1 minute) that actually came out pretty nice. I was even further surprised that there didn't appear to be any significant color shifts, considering the age of the film and the fact it was shot with a toy camera. I also didn't have that problem with the unexposed area around the frames coming out cloudy, they were black like they should be.
These will be fun rolls to just play around with, but being that processing isn't really cheap, I just wanted to make as many good exposures as possible. So from the info so far, it sounds like I should be overexposing the film a decent amount though, correct?