I cannot see on here the vendor of this product. If that is known it would be useful information to make public.
It is one substitution that might actually be hard to detect without testing, reta and tirz are not identical but most of their effects are pretty similar and dosing is also fairly close, so it would not surprise me at all if most people simply did not notice.
I have always found it fairly weird that there is not a lot more of this and other dodgy or empty vials, as the only thing stopping it is return customers to an established vendor "brand".