Outlook address file returns old data

I use Word mail merge with my Outlook contacts address book, filtering the hundreds of addresses sucessfully and then merging to create mailing labels. But....when producing this last label run, I noticed a small number of addresses were old data. I had updated these addresses weeks, even months earlier. The old address was no longer in Outlook, both on desktop and web versions. There was only one address type held, and this was correctly ticked as the mailing address. I have no idea where this old data is being held or accessed. Any thoughts?