{This/that vs. these/those} + many + plural noun

From pag 419 of Mastering English An Advanced Grammar for Non-native and Native Speakers:

Elsewhere, demonstratives normally serve as determiners (as in that exact moment, this way, etc.). BUT in connection with adjectives and quantifiers such as much and many, the singular demonstratives may serve also as degree adverbs, indicating a precise amount or measure:

(14) I didn't give her that much. (15) Do we need this many recommendations? (16) The worm was this long.

Yet, despite the number of stars in the sky being uncountable by nature, so no precise amount at all, the sentence I've never seen this many stars (in the sky) is uttered by the character "Ian" in an informal context in the last chapter of the fifth season of Shameless, "Love Songs (In the Key of Gallagher)".

Therefore, is the purported different this/these + many + plural noun still operating? Granted, "precise amount or measure" is quite subjective.

The difference between “much” and “many” is whether the thing measured is “countable”.

Stars are countable, they can be counted: one star, two stars, three stars, …

It may take you a while to count all the visible stars in the night sky, but they still are distinct stars you can count.

An example of something uncountable is sand. You can have too much sand in your shoes/in the playground/wherever, but you cannot count the amount of sand (although you can weigh it).

(Rice and grain can be both countable and uncountable: when you have too many grains, you have too much grain.)

There is also a difference between “this many” and “these many”:

• “these many”: the focus is on the thing (of which one acknowledges there are many)
• “this much/many”: the focus is on the amount or measure itself
• *“these much”: almost always wrong, unless in “these much-appreciated paintings”

Applied to example (15):

• Do we need this many recommendations?

  = Granted, we need recommendations. But do we really need as many as we already have?

• Do we need these many recommendations?

  = Do we need recommendations (of which we have many) at all?