(I am scheduled to be upgrading to 2019 sometime in 2046).
Meanwhile back at the ranch ...
I can't make the {INDEX \s } switch generate anything other than a zero. I tried with the \s string with, and without double-quotes.
I documented outside Eileen's Lounge "Unrelated, I think, to the {SEQ} field." but put the four {SEQ} fields in just in case I was wrong.
OK "{INDEX} switch anomaly" is a dead issue because
(1) I am 20 years behind the times and
(2) These switch failures are documented elsewhere on the web.
I note that some web pages basically reprint the Help files (https://bettersolutions.com/word/fields/index-field.htm) but their examples do not work (for me) in Word2003).
Bottom line: Do not assume that {INDEX} and {TOC} switches work as advertised.

Chris