Ok, that's good to have ruled out the smart quotes red herring.
If you already have an INT book in Paratext and want to dynamically import any of those \periph sections from that INT book into your FRTlocal.sfm file, you can use:
\zgetperiph|preface\*
\zgetperiph|introduction\*
to import the section(s) as needed. But make sure the option: "Use Peripheral Introductory Sections" has been enabled for it to import them:
There is no harm in removing the id="xxxx" parts of the \periph fields. As you say, everything works fine. Those are more important when certain periphs have to be inserted elsewhere in the publication (for example, an 'intnt' periph section gets inserted AFTER the OT and just before the NT starts).
If there's still something that isn't working as you want it to, please send me a small archive (select a small book, and then use the button on the Help tab to make a .zip file). Send it to ptxprint_support (at) sil.org for me to look at.