Ilford IN-1 Stop Bath

I received an almost full bottle of Ilford IN-1 Indicator Stop Bath. From what I can tell, it's an acetic acid stop bath. Ilford has discontinued this version and there is no info on their website. Per the bottle, it's to be diluted 1:31 (or 1:63 for economy for short printing sessions). The bottle references its use for prints, but not for film.

Is there a reason this can not or should not be used for film?

I use the Kodak version of acetic acid stop bath for film - diluted 1 + 63.
This old photonet thread talks about your stop bath, and includes the information (in 2003) from the Ilford website: https://www.photo.net/discuss/threa...tion-required-re-ilford-in-1-stop-bath.57445/
I find it interesting that there is no reference to use with film, but I don't know whether there was another Ilford product at that time with a different strength or packaging that might have been more suited to use with film. It may be important that the photonet thread refers to the market in Japan.
I would have expected a warning if your stop bath wasn't suitable for use with film.

I saw the photo.net post. It does describe IN-1 as acetic acid (as the Kodak product) and the later product as citric acid based. But that post is the only reference to IN-1 that I could find.

I could just use it with paper, but was curious.

You might consider reaching out to Harman - either through their website contact form, or via a Conversation with Harman Tech Service here on Photrio.