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.