most '60s homes do have grounded outlets
I think I said this before, but here it goes again: I have seen a single ungrounded outlet in any electrical system installed in recent decades. My current residence was built in 1965, and it has grounded outlets throughout. It was pretty cheap construction new, and any corners that could be cut probably were. I doubt it was ever rewired, based on the history I know.
The only place I have ever seen that might have had ungrounded outlets in newer wiring was the house I grew up in. Part of that house was remodeled, and the electrical system would have been redone at that point. It's been years since I saw that house, but I have a sense that it didn't have grounded outlets in the new part. But I have no idea when that wiring was actually done. Last remodel year was known to be in the late 60s, but whether the wiring was done at that time or earlier is anyone's guess.
Of course, this is all based on my limited observation. I do notice things like outlets. Also things like furnace technology, type of stove in the kitchen, and, oh, yes, brands of washing machines. (I bet I'm not alone in any of this here at AW.org!)
And, of course, this is based on Washington: codes vary. They even change here. I know of at least one person who built their own house, and got stung by code changes between the time they started wiring, and the time they were done and ready for an inspection.