Tasco was a brand as was Optima. At sometime in the 90's Hakko or whoever were making the Tascos sent their mchinery to Taiwan to continue the manufacture. Funny you I have two identical Tasco 3-9 x40 Prohorns one Jap and one Taiwanese, but I'd give the later 10% brighter.
It did seems that coatings and just something coud change from year to year with certain models.

With Optimas the first few years they came parallaxed to air rifle ranges. Later this feature changed to the standard 100m. Thankfully the design allows them to be parallaxed back. Some scopes do not have the space to more the front lens forward so they are stuck at 100m. Some scopes can and some can't be reparallaxed.
AO scopes that allow for ten to infinity parallax are the way to go. However, have a poor one and there can be POI shifts; really has to be made well.

In the early days a 4x40 was all air rifles shooters demanded. That was a huge leap from iron sights. It also showed up how poor rifles grouped once beyond the farmyard ranges. As shooters could get a sight picture on targets further out then they demanded more from their rifles. And more from the pellets too.

I agree the better Tascos were great. They didn't stay great and not every model in the line was equal to the task. Basically you had to pick the good'un model. Kassnar was another brand which started well and then went very average. The real change was the trade changed in 1992, and the who scope world was different again. Simmons hit the market with their WTC range.. the rest is history.

The early Optimas were well matched to the springers of the 80's. Good quality to price. By the 90's they lost out to cheaper and the fact they were showing their age. Really didn't matter what additional features or models they brought to the product range.
To me certain 80's rifles look the part when fitted with an Optima. HW35E, 80, 77, FWB Sport, Original 45, even Omega. Certainly German rifles of the 80's.