There's two Scriptures for Jade Emperor.

First Scripture is mend for the 17th Generation Jade Emperor, Second for the 18th Generation Jade Emperor (Existing Tian Gong).

I believe in orthodox Taoism, there is only 1 Jade Emperor - Yu Huang Shangdi.

His scriptures includes 'yu huang xin ying miao jing' and 'yu huang ben xing jing'.

Yes, you are almost right in some way, in the heaven or in the whole world, they can only be one Jade Emperor (which believe to have a surname of Zhang).

But as time changes, more people to believe that the old Jade Emperor had hand over his throne to the existing Jade Emperor ~ Xie Tian Da Di (Guan Gong).

Since this is worship, respect by the folk Taoism in the mortal world, it is a fact that we can change or sudden withdraw from the chart.

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Something to add in here, in Taoism, there's no such theme as orthodox Taoism or unorthodox Taoism.

Such theme is given due to personal jealousy between seniors, sects, etc.

In whole, all small sects, diff sects, still go under the Big Taoism Umbrella/Family.