There are some general rules about when a "the" is or is not required.
Plural nouns referring to specific things
In the specific three examples you provided, the inclusion or exclusion of the "the" is largely just a matter of personal preference, or personal style in writing, for two reasons. First, all the nouns are plural. Second, they are all referring to specific examples (e.g. data, fluxes and results in 'Table 1').
Since the "the" is optional where both the above conditions are met, all of the following pairs are acceptable.
Example 1
- The data points in Table 1 were assembled ...
- Data points in Table 1 were assembled ...
Example 2
- Fluxes shown in Table 1 ...
- The fluxes shown in Table 1 ..
Example 3
- The results of the calculations indicate ...
- Results of the calculations indicate ....
Plural nouns referring to general things
By contrast, where the noun is plural AND it refers to a general not a specific thing, then it is conventional to exclude the article. For instance, the following sentence would always be used without the article.
- Housing prices in the US have ...
- Inflation rates in coming years will ...
- Houses of Parliament around the world are ...
Singular nouns need a "the"
If the noun is singular, a "the" is almost always mandatory, because it is referring to a specific thing (which is why the term for the word "the" is "definite article").
For instance, if your examples were modified to have a singular noun, the only correct expressions would be as follows.
- The data point in cell D24 was obtained ...
- The flux value of 0.1247 in Table 1 ...
- The key result of our calculation was ...
You will note that in my reworded version of your example 1, the word "data" has been changed to "data points". The purpose of the change was to avoid the debate about whether the word "data" is a singular or plural noun. Most authors would treat it as a singular, but there is still some debate (see, for instance, this article: https://www.theguardian.com/news/datablog/2010/jul/16/data-plural-singular).
The distinction is important, because if "data" is singular (like the word "datum") then:
(a) it must have a "the" preceding it, and also
(b) it needs a singular verb.
In your first example above, the author has used the verb "were", which is a plural verb. This means that the author is treating "data" as plural noun, in which case the "the" is optional.
But it's way more nuanced & complex ....
The above general rules are just a starting point ....