Chapter 9 of my free book on QP formulas, functions, and macros deals with conversions between text and numbers, including an article on @DATEVALUE. It contains an article with a number of sample formulas entitled "How to convert text dates/times into numeric dates/times." Several of the samples are close to your example.

It would be great if Corel would expand the formats that @DATEVALUE can use. That would make this common task simpler.

Construct a working function in a cell to the right of the first cell in your range of cells. Then copy that function down (usually) in parallel to the entire range of date-text cells.

The book is here: http://corklaw.com/Tech/QP/QP_FormulasFunctionsMacros.pdf

Charlie