Hmmm, yes, I've seen some of this -- except the slides are mine from the 1960s, not my grandfather's!
I have scanned a few for my PBase galleries, with intent to do more, but was surprised at how much work was involved due to needing major tweaking. Even some that were on Kodachrome did not appear nearly as good in terms of color as I remember them. Makes me wonder if there may have been some occasional substandard processing involved, as I did sometimes go with discount mail order places.
The early ones that I have scanned were taken with my Argus C3 -- the Brick. And using Sunny 16 in the beginning, probably not recommended with Kodachrome! I hope one of these days to tackle some from the mid-60s taken with my Konica FP and see what they look like after all these years. I think I had largely switched to Ektachrome by then, so that could turn out to be a different source of disappointment. Some Anscochrome out of my Minox from the mid-60s that I home processed has faded and color shifted a lot. It took everything I know (which may not be all that much!) to even approach a decent scan from them. Not to mention an 8 x 11 mm frame ain't very much data.
Sometimes I think of old family photos not as records, but as memory triggers. For that they don't have to be perfect!