dvr disappearing recordings

My recordings keep disappearing too.  My DVR says it is only 33% full.  When I count the total hours of saved recordings, it is about 75 hours and my DVR is supposed to have a capacity of 150 hours.  It has finally dawned on me that the choice provided by Xfinity of "Until space is needed" is, counterintuitively,  a shorter time period than the other choice of "For 1 year."  As others have pointed out, we sometimes keep older recordings because we want to view them again.  Even if they are available on a streaming platform, I would rather play my recording so that I can fast-forward through the commercials.  And you never know when a streaming platform will stop carrying the movie or show you want to see.  I guess it's all a crapshoot and we might as well think of our outrageous cable bills as a gambling debt.