AP Tax Code

[rb123v]

Invoice date is in between the tax code effective dates there is no problem.
If the old paid invoices date is after the tax codes end date, I am not able to access those invoices through invoice workbench. When I try to access distribution lines I am getting error saying tax code is invalid.

I should be able to access old paid invoices even after tax code is end dated. What is root cause for this problem? Is invoice workbench verifies tax code status when I query invoices?

if tax code is disabled in expense template, can I use same tax code in expense report creation?

Is tax info mandatory at the of creating expense report? If its not mandatory at the time of creating expense report, will tax code be generated at the time of expense report import program? if so what
program generates tax code?

Please clarify above questions.