I have migrated my old 2.16 MRTG environment in a RHEL 6 machine to the new 2.17.4 a while ago and I keep having the same problem, my day, week and month graphs are updated as they should be with crontab but the year graph is not.
When I first updated the system I didn't copied from the begining all the images from /var/www/html/mrtg so they started to be generated and I also ran a cfgmaker to creat the new mrtg.cfg file. Then I copied my old mrtg.cfg file and also all the .png day, week, month and year pictures into /var/www/html/mrtg and I ran a indexmaker command to make the change happen and it does for one day. The year graphs are updated once a day but whenever the crontab does it the graph goes back to its old historical year graph which I had removed.
Does anybody know how could I make the change permanent? I haven't tried to recompile all MRTG but is going to be my next step.
I have found an answer, I have just to update the ".old" and ".log" MRTG files who generates the historic data.
https://lists.oetiker.ch/pipermail/mrtg/2007-October/033185.html