Measuring spoons should equal in quantity to measuring cups, correct?

Situation, I have been using plastic measuring spoons for years. They
are made by Echo I believe. They are flat and rectangle shaped. I use
these because they fit into my spice jars. Through the many years of
great service they have become very worn and I thought I would update
them. I cannot find these spoons anywhere but, I found some really
nice stainless steel measuring spoons that are designed to fit into
spice jars and they look really nice, BUT, they are not the same
measure as my plastic spoons.

What I mean by this is the quantity in the plastic spoon when poured
into a metal spoon overflows by quite a bit.

I did some testing with several spoons and cups to attempt to see what
was more accurate with little success.

8 Tablespoons equals a half cup! so I used the plastic spoon to
measure 8 Tbs. of sugar into a half cup measure and it is very close
but when I do it with the metal spoons, not even close. I also tried
with teaspoons. the plastic comes very close but the metal is lacking.

I also have tried different brands of measuring cups and they do not
measure equally either. One cup with plastic does not equal one cup
with metal.

I have two sets of metal spoons, Endurance brand and William-Sonoma.
All of these spoons are made in china even the plastic.

How do I know for sure that when I put two tablespoons of sugar in a
recipe that is in fact two Tablespoons? or if a bread recipe calls for
two teaspoons of yeast that I am adding the correct amount.

I thought the United states has a weights and measure office or
something. shouldn't they be on top of these imports?