You should learn to be a bit more trusting. Why do you suspect that Ilford, a company that's been in business for decades, has a good reputation and is a leader in the industry, would sell you a stop bath that would stain your prints? And why should you doubt their capacity recommendations?
Furthermore, technical data sheets for all Ilford products are easily available from their website or by just Googling the product name. Here's the one for Ilfostop:
https://www.ilfordphoto.com/amfile/f...5/product/669/
Best,
Doremus
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