A neat Belgian article on how clues were there, but were missed before the murderous attacks in Paris in November 2017:
About one clue, however, nothing has been published yet — and that clue is likely the very best chance authorities missed to detect the terrorist cell....a subsequent house search a handwritten note was found. It seemed of little importance: “Bayroshock without chlorine”, it mentioned, followed by the addresses of two shops for swimming pool equipment in the North of France. Bayroshock is a product against algae that consists of hydrogen peroxide at a concentration of 34%. Apart from being recommended for the treatment of pools, that same substance is also a main ingredient of TATP.
Not being avid watcher of limiting explosive components:
An EU Directive (2008) banning the sale of hydrogen peroxide in concentrations above 12% to private customers was passed into law in July 2016 (in Belgium). But in France, a softened version entered into force last year, just requiring registration for private purchases.
The author is:
a journalist working for the Belgian newspaper Het Laatste Nieuws

That makes me wonder have other nations followed this dilution of Bayroshock?

The UK has, as this advert clearly states:https://www.onlinepoolstore.co.uk/ba...nly-4709-p.asp

There is a catch-all thread on General CT where this may sir one day. See:http://council.smallwarsjournal.com/...pe-(catch-all)