No. Please read Stosh’s #21, and you’ll see what I meant.
I do not count nucleotides that have only been produced in a lab as part of the nucleic acid alphabet.
We have been using inosine in DNA sequencing for decades to help with “reading” difficult regions (for instance, those with a high GC content). But I do not know anyone who counts inosine as one of the nucleic acid letters.
While the artificial nucleotides might have utility in research, since they do not have biological function (at least within the DNA/RNA systems), they should not count as letters.