Several formulas have prebiotics in them (I don't think any available in the UK have probiotics) and the precise combination of whichever one is used is indeed owned by the companies and not shared. So the C&G reps were sort of right, JollyPirate.
Formula is a commercial product - just like any other industrially-produced and packaged food and drink, the 'recipes' are not shared with competitors. The slight differences in formulation are presented as significant in ads in healthcare professional journals. The differences have to be slight, as all formula has to be produced within legal parameters to be approved for sale...no manufacturer could start selling something way out.
I think it's likely that some formulations suit some babies better than others, though there is no independent research on this. Breastfed babies get 'tailor made' milk whose exact fat content and antibody content and volume and flavours and so on is unique to them and changes as the baby grows. Formula fed babies get the standard product every time, so it makes sense to accept that even slight differences in taste and ingredients may be significant to some of them, some of the time.
The research on specific 'comfort' and 'easy digest' milk brands is not in the public domain (though low lactose formulations and the addition of prebiotics have been shown not to affect growth adversely). I think it should be - commercial interests be damned. If something has been shown to be beneficial to formula fed babies, in general, then it should be in all formulas. If it only affects a few, then parents should know that, too.
If I was a formula using parent, I would be very cross that all I can go on is trial and error and the anecdotes of other parents