Basically, yes. One hit (as in the: the amount of LSD typically found on a typical blotter square) = roughly 100 micrograms, probably less most of the time.
It seems weird to put such a small amount in a vial, since 2 blotter squares would be infinitely easier to transport, though I suppose you could maybe use it for precisely measuring out microdoses.
If it really only contained 200 micrograms of LSD in solution, then yes, it seems plausible that whatever is left in there could be around the strength of a microdose, i.e. ~10 micrograms.
If there was crystalline LSD in it, though, then it is very unlikely that it was just 200 micrograms - 200 micrograms of solid crystalline LSD is such a tiny amount that it would be a speck of dust barely visible to the naked eye; you don't wanna wash it out and ingest it, only to find out that the vial used to contain 200 milligrams, and there was still more than a whole milligram - i.e. 1000 micrograms - left.