So far, the problem seems only visual (such as viewing old invoices). Could this rate update have any adverse affects when making reports for last year?

It would be great if we could assign dates to tax values, much the same way exchange rates have dates.  I saw a suggestion on a different thread to create different tax groups for different dates.  But this would be quite convoluted and I don't really see it as a legitimate work-around. It would require admin of every customer (updating applicable tax) each time the tax changes.  For those with hundreds of customer, this seems out of the question. Furthermore, in Canada, where we have a tax for almost every province, changes happen often and the burden would be great.