“People started keeping relatively widespread careful measurements at the end of a little ice age .”
Little Ice Age is usually defined as ending about 1850, some say earlier. In 1850 accurate standardized weather measurements were being conducted mostly in Europe, East Coast of North America, some on the West Coast. A handful of other places would have existed in North and South Africa, Australia, New Zealand, some parts of Asia and a few other spots, but no global coverage by any definition. Not until WW2 was there anything close to global coverage. Really global coverage started in the 1960-70’s with space based measurements. At best we have less than 100 years of good records.
Just the same, the LIA, of indeed the MWP before it, can either be viewed as representative of conditions beyond Europe and the North America or an exception to it.
I’ve heard Greens try to say it was an exception in either case, a result of conditions localized to the Atlantic ... but that seems a rather self serving stance for them to take seeing that they want to attribute whatever the climate is doing to humans harming it.
So it is not necessarily the case that less data doesn’t mean bad or non-representative data from which trends and conditions beyond can not be reasonably inferred.
Please keep in mind the climate models the current lot are using have been pulled from their collective asses and that when dealing with the likes of the IPCC they were given the politically determined objective to find anthropogenic warming and that is exactly what they found: surprise, surprise!
Never trust bastards.