I'm further encouraged by all your replies to go with the death date on the certificate.
I have been through the burial records for the church concerned but either missed this one or failed to record the details, another trip to my local LDS centre is called for.
The headstone inscription wasn't from MI's, I stood before it myself and took the photo but I do remember at the time thinking something isn't right

.
I've not gone down the track of looking for a death notice in a local newspaper mainly because they are not accessible to me, but it may be something to do on a future visit to Cheshire.
Thanks everyone for your help.
Sue