K-type temperature adapters for DMMs and how much of error they add-up?

[Kiriakos GR]

In the past five weeks I do explore K-type thermocouple and connectors. 

Its interesting of how strict is the science of measuring temperature, about the use of only the appropriate connector type according to sensor type.

In order any K-type thermocouple to get connected to DMMs, it is required a relative adapter this terminates to banana plug.
FLUKE, Keysight and a few more has relative offerings, but the most interesting part is that these accessories they are circulate as totally undocumented.

Here is a pack of unanswered logical questions:
How much of error they add-up? ( they are dissimilar metals aren't they ?) 
From what metals they are made of?
 
At my first DMM of 90s, there is on-board a K-type slot, inside they are two set of copper blades.
It works but measuring error specification at specific DMM this is significant above 50C, and it might be that way due electronic parts age / old technology.

The point is that when at thermocouple wire we use copper plug for termination and connectivity to a measuring device, does it really matters?

The only given specification this is plastic insulation tolerance:
Suitable for low voltage applications (below 30 V ac, 60 V dc). 

From the era of Agilent Technologies, we have the text bellow:
For a quick measurement, use the 0 °C compensation adapter to see the temperature variation of the
thermocouple sensor.
The 0 °C compensation adapter assists in measuring the relative temperature immediately.
(non-compensation transfer adapter)

[Kiriakos GR]

Unbelievable !!
At the point that our Electrical test and measurement corporations and or measuring instruments sellers, failed to deliver a piece of clear answer, someone at Texas Instruments he did wrote an interesting read about thermocouple - analog measurements.

I did a good study of all that about Cold-Junction / ice point / isothermal  etc,etc. and in theory there is no problem of what will made of, the adapter which will connect a K-type male within a thermometer.

I did tested three different K-type temperature adapters for DMMs, and all are made of from clean copper and nickel plating.
Second in the row test, metal composition of several K-type male plug (the ones arriving over unbranded K-type thermocouple), all use some-sort copper pad and nickel plating.

The bid exception here was a real OMEGA thermocouple, at the cold junction side the pin it was attracted by a neodymium magnet, while the other pin (aluminum) this was immune at magnetic traction.
I am now convinced that all OMEGA connector are made under the concept of inline extension.
And due this reason, all OMEGA connector they are made by the concept of respect at cold junction side no matter of how many extension connectors they might be used per thermocouple singe line.