As an FYI, the following disclaimer is at the bottom of the Tax Center page:
Note: The information on this page may be based on estimates and shouldn't be used for tax-reporting purposes. Refer to your Vanguard tax forms for final reportable income.
Secondly, I believe there is some serious confusion in this thread about the accounting of dividends in this account.
There are three dates for dividends for ALL mutual funds.
1.) Declaration Date (this is the date that defines what year a dividend is taxable.)
2.) Reinvestment Date (if you have auto reinvestment, this the date that the dividend is posted and recorded in your account.)
3.) Payable Date (the date a dividend is posted to your account if it is not reinvested, or is distributed externally)
The Tax Center, correctly as far as I can tell, assigns all dividends to their correct tax year.
The Tax Center correctly records the dividend's accrual as per the rules you have assigned to the handling of the dividend. It does not predict the future, but it correctly reflects that past.
The transaction history (instruction errors not-withstanding) reflects the date or each dividend as per the rules above.
For example, VBTLX had a declaration date of 12/31/18, a reinvestment date of 12/31/18 and a payable date of 1/2/19. that is all correctly handled in my account that had a non-reinvested dividend.
The key here is to understand that Dividends have 3 dates related to them and there are nuances that can have consequences, especially at the end of the year.....
I have dividends for stock funds, bonds funds and money markets that are both reinvested and payable to settlement accounts (IOW, my accounts have representative sample of all reasonable cases except dividends being paid to an external account)
The other concern is that Vanguard does not have "up-to-date" balances until very near the opening of the next trading/business day, with the exception that most Saturday's things are good as they would be for Monday. Any balances, transaction history, etc. is not complete between 4pm at close until somewhere near 9AM the next morning.
I don't have a current brokerage anywhere else these days to compare, but my credit union, bank, and credit card providers cannot be considered anymore timely than that. In fact my credit union is bizarre because they sometimes post items in the future, but make them look like today and that messes up my account tracking horribly if I am not watching for it.