Comment by falcor84
I would think that it's more like a general codebase - even if after 2.5 years, 95% percent of the lines were rewritten, and even if the whole thing was rewritten in a different language, there is no point in time at which its value diminished, as you arguably couldn't have built the new version without all the knowledge (and institutional knowledge) from the older version.
I rejoined an previous employer of mine, someone everyone here knows ... and I found that half their networking equipment is still being maintained by code I wrote in 2012-2014. It has not been rewritten. Hell, I rewrote a few parts that badly needed it despite joining another part of the company.