Endocrinologists do vary, I had one that started me on Armour. That was in another state where I lived at that time. She also knew the charts out there are super super conservative and correct amounts really differ from those charts, she knew how to calculate the correct amount. Where I live now there aren't any Endo that handle Armour, so my primary care does. I do see Endo for the cancer part. What I hear in your info is real common to hear, it shouldn't be though of course.

Some info from a blog at https://biomedee.blogspot.com/

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What are the equivalent amounts to switch from T4 only to NDT (middle of a bell curve)?

With NDT we use the word "grain". 1 grain of NDT has 38 mcg T4 and 9 mcg T3 in the USA. The listed mg of a grain depends on brand such as Armour or Nature-Throid. A grain can be 60mg or 65 mg (which is not an amount of T4 or T3) and again depends on the brand as to the mg but not the amount of T4 and T3.

This chart is aimed at the kind of middle of the curve group where 1 mcg of T3 is about like 2.5 to 3.5 mcg of T4. It does not represent all people, just kind of the middle of the bell curve. Amounts to swap are dependent upon each individual and how T3 works on you. With that in mind, the middle of the bell curve group suggests swaps having 1 grain equal about 60 to 70 mcg T4. You very well may need more or less if you take very large amounts, or very low amounts, of T4 to work for you and you are of normal weight:

100 mcg pure T4 calculated 1.4 to 1.7 grains: Low possible 1.25 grains, average 1.5 to 1.75 grains, high possible 2.0/2.25 grains
125 mcg pure T4 calculated 1.75 to 2.1 grains: Low possible 1.5 grains, average 1.75 to 2.0 grains, high possible 2.25/2.5 grains
150 mcg pure T4 calculated 2.1 to 2.5 grains: Low possible 2.0 grains, average 2.0 to 2.75 grains, high possible 3.0/3.25 grains
175 mcg pure T4 calculated 2.5 to 3 grains: Low possible 2.25 grains, average 2.5 to 3.0 grains, high possible 3.5 grains
200 mcg pure T4 calculated 2.85 to 3.3 grains: Low possible 2.5 grains, average 3.0 to 3.5 grains, high possible 4/4.5 grains

Once again, you split this in two, taking half first thing AM and half in the afternoon or some variation like in thirds, etc.

Those who do not absorb synthroid that well and thus take larger amounts are further out on a bell curve and would have differing numbers than above. For them 1 mcg of T3 might have the effect closer to 5 or 6 mcg of T4. This would be very possible but is less likely. So keep in mind the chart above is middle of the curve and if you are taking very large amounts of synthroid with a normal weight the chart above may not apply to you but it may be possible to adapt it knowing you take double the amount of synthroid than others your weight for example.

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But the charts give a different equivalent for NDT, why is that?

Equivalency charts are designed around a highly conservative view that the highest possible effect should be listed in equivalents in case of side effects, trouble is that can raise TSH and leave you feeling lousy. Because of that basically there are charts out there giving incorrect amount of NDT to replace pure T4 even by conservative measures. These charts say 1 grain has the same effect as 100 mcg T4. This is just not the case. 1 grain of natural thyroid has only 38 mcg T4 and 9 mcg T3. This cannot have the same effect as pure 100 mcg T4.

From the calculations below you can see that for most people 1 grain of natural thyroid (USA only) has the effect of somewhere in the 60 to 70 mcg area of straight T4 only.

38 + [9x (varies by person but try 2.5)] = 38 + 22.5 = 60.5 T4 equivalent in my case because 1 mcg T3 has the same effect for me as 2.5 mcg T4.

38 + [9x (varies by person but try 3.5)] = 38 + 31.5 = 69.5 T4 equivalent in a person where 1 mcg T3 has the same effect as 3.5 mcg T4.