These tabs will very likely have been produced specifically for the purpose of microdosing. The standard dose for these microdose tabs tends to be 10 ug, so not far off.

I usually dose 10-15ug as a microdose (accurately) and I find this the optimal dosage every 3 days. Every two days was too intense and the doses stacked. I think like standard LSD tripping its different for everyone and about personal preference. I found microdosing takes a lot more experimenting than LSD to find the sweet spot. I'm going to give a lower dose like this a try, thank you.

http://www.wedinos.org is another site which provide LSD blotter testing results. However they do not state the dosage. Worth a look though.

Superinteresting.
Thank you Endlessness.

Just as an addition. Here the overall testing results from the free drug testing center DIZ.

IMHO interesting to note, that in the years 2014/15 more than 40% of the tested blotters did have less than 50ug on them...

But one also has to note that the sample size isn't very big.

Unfortunately couldn't find the newest data.