Sorry for creating confusion.
Today I wrote a note on the iPod Calendar for 4 Jan 2016.
Soon after I can see it on my iMac in front of me - this is by Wi-Fi. And it hstillremained on the iMac Calendar.
But then I find the original note on 4 Jan 2016 on the iPod has been removed from my iPod.
I have since discovered that all the notes prior to 15 Jan 2016 on my iPod Calendar have gone. They remain on the iMac.
Yet the all day events in my iPod over the last year are present.
I have tried using "sync" with a USB connection to yhe iMac but no change of data on the iPod.
Today (30 Jan) I put a note into the iPod - it transferred to the iMac - and remains on the iPod!
But I need to get all the data prior to 15 Jan 2016 back onto my ipod but how?
Thank you for your help.