However the alumnus tag has now been put through the mangle by those on the youngest continent currently on the planet, then put back through the mangle to give it a 'special' tag.From this spews the 'heritage' label, 'a pupil'.
Those that teach (schools, through further college up to universities) are quite entitled to use alumni for all that have passed through their gates and onto life in general despite achievement, qualification or even finishing a course, anyone undertaking the journey is entitled to be called an alumnus (though the Latin changes wrt gender - see alumna)
There are however a spattering of bit-part companies using the term 'alumni' for staff (past and present), offering status to those that have favo(u)rably passed through the business onto better things,or are still in the loop, but denying the status to those that have severed contact (those now left the industry completely, are beating them in competition or came to disagree with the business operandi of those that employed them), despite conforming to the true definition of 'alumnus'.
Whilst the term 'old boy' could be criticised for a gender issue, substituting it for alumni confirms they either
1) fail to understand Latin,(justifying ridicule for having used the term in the first place) or
2) believe that some misplaced hijack of the definition in the 21st century is acceptable, (in which case ridicule is guaranteed for all time).
In many ways the modern company usage of the word is similar to 'old boy', if you are curently of no use, then you are worthless.