So with oldbloods you have the on foot version, and the one on a Carnosaur. The Oldblood on foot allows saurus models with in 5” to reroll wounds of 1, note with the key words “You can re-roll wound rolls of 1 for Saurus models within 5" of an Oldblood.” as the warscroll does not mention if the Oldblood is in foot or on a carnosaur, so would the Oldblood on Carnosaur also get the same rule due to key words?
Oldblood isn't bold in that text, so it's not a keyword but a reference to the actual unit. So no the mounted variant doesn't get it. Also, it'd be weird and definitly not intended. probably just a relic of the old (inconsistent) ways of phrasing things.