Yes 6 months is the usual time to dispose of them but Im like you after 6 months mine are fine but I notice that the parts start to fall off easier and that gets irritating but I have come up with a plan, every six months Ill get 6 new pari cups and then the six that are ready to be disposed of I keep in a zip lock bag for back up incase anyparts from my other set goes missing or gets melted then after six months I throw them away and put another old pair into the zip lock bag.
I have a total of 18 pari cups I use, 6 for pulmozyme, 6 for hypertonic saline and 6 for tobi. I mark all the neb cups by the month I got them in and I found out that if you put the thick tape like clear duck tape around the marker part then it stays a lot longer and doesnt wash off nor does the tape come off, makes it so much easier to keep it all together and organized. ON off tobi months then I split the cups up between pulmozyme and HS. I also have the nebs marked with a P for pulmozyme HS for hypertonic and then I dont mark the neb cups with tobi, I guess i could put a T but nnaaww.
Hope that gave you some ideas on what to do with your neb cups at least this way works pretty good for me.