Can a sole proprietor wait until AFTER December 31 to make (deferral, as well as matching) contributions to a SIMPLE-IRA that was established prior to the October 1 deadline?

In Publication 560, the IRS defines self-employment income in terms of Schedule SE, but that number is not known until after year-end.

Yes. For the unincorporated business owner.
If the business owner has common-law employees, their salary deferral contributions must be made from their paychecks and deposited to their SIMPLE IRAs by the 30th of the month, following the month to which the deferral applies. For instance, salary deferral contributions for November must be deposited by December 30, and those for December must be deposited by January 30.