There is the NAN Pelargon that is usually used for HIV babies as it contains more iron that normal Nan (orange tin)
Then there is the normal NAN (Blue tin)
NAN HA is more expensive and is hypo allergenic, thus if there is a history of allergies this would be the besxt route to go.
NAN HA has a higher concentration of Vitamins and minerals and I think it has HHA and DHA (I stand to be corrected)but some babies can fidn this too rich (like my son did) he was on S26 Gold and it gave him cramps etc but S26 didn't.
It really is a hit and miss with getting the right formula, my advice is buy a small tin of the Nan (blue tin) and see how baby responds to it, if it doesn't work, move on to the next formula, but give it a couple of days to settle before moving on.