Maybe I'm not understanding the Rule of 75. I took it to mean You Age + Leng
of Employment = 75 years.
With a birthdate of 10/1/80 and a hire date of 6/5/06, on 2/1/2031 you would
be 50.33 (50.36 if you don't figure in the leap day) years old and you would
have worked for the company 24.66 years (plus a bit extra in both cases,
which puts you at 74.99 (and a bit) total age+length of employment. If you
add one day ( =TEXT((27393.75+A2+B2)/2+1,"mm/dd/yyyy") ), you're over 75
years (age+employment).
On June 4, you will be 50.67 years old, and will have worked 24.996 years at
the company.
Seems to me to be a rounding issue. Likely the case with the other formulas
as well.
If this doesn't work for you I can try to make this less accurate?