After I posted the above, I created the following columns which works close (for now)
1. Orig Hire Date 1 = DATEVALUE('Table'[Orig Hire Date])
2. Today = Today()
3. Calculated Measure Diff2 = [Today].[Year] - [Orig Hire Date 1].[Year]
The above works BUT Sum of DIFF2 gives additional years of service because it calculates those less than a year of service as 1. The correct answer should be 305 but Sum DIFF2 gives 339.
Any ideas of refinement from the above DAX is appreciated.