it is not meaningless
these are Joola branded, not some no-name brand of which you are probably referring to.
I see Joola advertise 1, 2 and 3 star training balls. and then 3 star ITTF approved balls.
I assume for them to have 3 tiers of training balls, the quality control also have 3 grading.
what doesn't make sense to me is, here is the link of the 3 star training balls
the orange has 3 star
the white is no star rating
The JOOLA Advanced Training ABS Balls are universal for all training situations. Made of ABS material with seam, the 40+mm balls are highly durable, making them the perfect high-quality, 3-star training table tennis balls for recreational or club use. Available in white or orange. Please note...
joola.com
to me, there are likely two different products, but under the same product page. extremely confusing