Sejobero, A systems End of Life date isn't set to a specific date for all systems of that model, a system is seen as End of Life when it reaches 5 years from its ship date. Under certain circumstances it could be longer, but that is based on part availability, but for the most part it is 5 years from that specific servers ship date. Hope this helps.. 
Can anyone advise the end of life date for Poweredge r520?   Thanks.
DELL Poweredge r520 EOL date