I might not know what heirloom really means because it's hard for me to think of a purchased watch as an heirloom. (From the post though the Seiko is clearly the one that has the strongest familial connection.)
A piece of furniture a grandfather made feels more like what I think of as an heirloom. Something one-off, made by the person you are remembering. But also a letter my mother wrote, her handwriting, is more valuable, more heirloomish than whatever the most valuable thing is that she owned.
It just occurs to me that I'm sitting in my grandfather's recliner chair right now, a very early model, from a local factory, of what would eventually become a fairly well-known piece of industrial design worldwide. I should probably have it repaired a little.
A piece of furniture a grandfather made feels more like what I think of as an heirloom. Something one-off, made by the person you are remembering. But also a letter my mother wrote, her handwriting, is more valuable, more heirloomish than whatever the most valuable thing is that she owned.