Having Vanguard export 18 months is considered very liberal. Some banks will download only 3-6 months.
If you don't have the last eight years somewhere (like in another software app), you will have to take the old transaction log and enter it manually, if Vanguard won't give it to you.
You can try a manual download from the website, but again 18 months is pretty liberal. I tried "custom dates" and put 2000, and it said "18 months maximum".
I was able to get a pdf back to 1998. but again, that would be manual entry.
My own recommendation would be to pick a date, enter the securities and balance, and go from there.
Thanks. It does turn out that one can copy the tabular representation of the data off the historical transaction display and import it to a spreadsheet. How one goes from that into Moneydance, I'm still not clear on.