so it's around 5 cents on C6 and 11 on C7. It's not crazy for a VCO.
Are you perfectly in tune in low octaves? you can maybe very slightly turn the slope trimmer. It will make low freq a bit sharper, and High freq a bit flatter.
Anyway, you can get a little bit better than 11cents on C7 but it will never be perfect on the whole range.
By the way, I think the NordLead is a Virtual Analog, not a real analog. If so, it's of course in perfect tune everywhere, but that's a different technology.