OH yes - the more you play with LTZ-type references, the more you realize you can make all sort of stuff unintentionally: Radio receivers, thermometers, seismic and vibration detectors, board stress detectors, barometers, board cleanliness measurement units, resistor drift test equipment, etc.
That's why I was asking about the choice of Non-A LTZ - remember those especially can be micro-barometers and board stress detectors - those internal wire bonds are more sensitive to the outside world mechanical stresses than the 'A version. Also you will need to adjust that extra TC resistor for your thermal flow situation - and if you're not using the datasheet resistor values you'll need to also adjust the TC resistor for best operation at -your- ambient temperature, enclosure and environment.
In the long haul over years and decades, we've never seen one LTZ type - be it A or Non A - outperform the other in terms of drift or noise. Either one can work well and we've plenty of examples where they just run very well inside datasheet specs. The non-A does require a bit more fiddling but can be good for very controlled environments, and the 'A is easier to get running on a production basis - and a lot more forgiving in real world apps. That's why a lot of manufacturers stick with the 'A.
I'm looking at a hard-working 3458a that has an 'A in it, the usual 15k over 1k heater ratio and LT1013 in plastic DIP - and it doesn't move a PPM or so annually, and has worked that way for years. The datasheet circuit values is a very good starting place for learning how these work.
And a PPM drift is almost impossible to -accurately- measure anyway in any real-world situation, if you add up all measurement uncertainty.