When you get into complex formulas, the syntax gets quirky really quick.
Your option in an If Statement structure should work they way you wish:
If(
ToDate([Date Created])<Date(7/1/2020,1,1),("E" & Right(ToText(Year(ToDate([Date Created]))),2)
&("-" &([Envoy PN 2019])))),
If(
ToDate([Date Created])>Date(7/1/2020,1,1),("P" & Right(ToText(Year(ToDate([Date Created]))),2)
&("-" &([Envoy PN 2019])))),
null))
the null part might be "", depending on field type, but you get the idea.
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Ryan Stanford
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