Read the unit before comparing the number
R-value describes thermal resistance; a higher value indicates greater resistance for the material or section represented. U-factor describes heat transmission; a lower value indicates less heat transfer through the tested assembly. The published garage-door values should not be treated as simple reciprocals because the test and calculation represent different things.
Ask which assembly the data covers
Keep the manufacturer’s data with the exact model and options being quoted. Ask whether the reported value represents a section calculation or a tested complete door. Hardware interfaces, section joints and perimeter construction are part of the complete assembly; an attractive core-insulation number does not describe every heat path.
Use the result for a specific buying decision
If comparing two proposals, request the same type of thermal information for each. Discuss how the garage is used and which comfort problem you are trying to address. Neither figure by itself promises a particular garage temperature or household energy saving. Glazing choices and the rest of the building still matter.
Your questions
Can I convert a published section R-value into the door’s tested U-factor?
No. Those published figures can describe different scopes and methods. Obtain the relevant assembly data instead of applying a reciprocal calculation.
Does a verified thermal value prove wind resistance?
No. Thermal performance and wind performance need their respective product documentation. One does not establish the other.