Regina found these errors in the latest OpenFormula draft. Thanks!

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6.18.41 LINEST
The indices in R² are still wrong. It is correct in https://issues.oasis-open.org/browse/OFFICE-3948 in the proposal. You can copy&paste it from there.

6.18.18 COVAR
The 1 in n1 and the 2 in n2 belong to the parameter name. Therefor the bar over them has to include the 1 and 2 respectively. You get it correctly, if you always write {n1} and {n2} in the formula editor.

The multiplication inside the sum is written as dot, therefore the multiplication outside should be written the same way, which means cdot instead of times. In other formulas we have written the fraction with over, I suggest to write here too {1 over N}
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correct as shown.