I made my post just to point out that thermocouples and thermisters are unsuitable for precision temperature measurement compared to RTDs and that has been the case for decades. But even with their complexities like cold junction compensation and lower accuracy, thermocouples are preferred to RTDs because of their temperature range and price. RTDs have the advantage of at least an order of magnitude better accuracy. They do make "precision" thermocouples by using purer metals but accuracy is still limited by the cold junction compensation and they cost as much as an RTD solution making them only suitable for when you need increased accuracy outside of the temperature range where an RTD can be used. I was not addressing the use of RTDs 100 years ago but I can.
The need for a stable reference resistance is not unique to RTDs and it is hardly a problem; we have been building resistors out of Manganin which are stable over temperature and time for more than a century using the same construction techniques used to build RTDs. I have a pair of ESI impedance bridges which use wrapped wire (probably Manganin) over mica resistors (ESI made these in house) built in the 1960s which are still accurate to 3 or 4 significant digits. It is not real clear how accurate the bridges are because they are as good or better than any 0.1% resistor (or capacitor) that I have tested them with and that is about the limit of their precision anyway.
An accurate RTD thermometer without amplification or stable voltage or current sources could have been made 100 years ago using a balanced bridge, Kelvin Varley divider, and galvanometer. As a matter of fact, my old ESI impedance bridges work in exactly this way for DC resistance measurements; no stable reference voltage or current is needed and no amplification is needed.
This would have been pretty cumbersome way to measure temperature because you would need to balance the bridge for every reading and consult a chart to remove the non-linearity of the RTD so if you only needed 0.1F resolution, a mercury thermometer would have been better if only because of its ease of use in an adverse environment.