The rest of Westeros thinks Dorne has 50,000+ spears, Quentyn tells Daenarys that Dorne has 50,000 spears, and yet Doran tells Arianne that they only have 35,000. I get why Doran would let the other kingdoms think that Dorne has more men than they actually do, but why would Quentyn lie to Daenarys. Nothing good would have come out of that (do you really want to piss off a girl who has three dragons?) unless Dorne actually does have 50,000 spears, or at least close to that number. I'm inclined to think that Doran would have eventually hired sellswords or relied on his alliances in Essos to augment his army to bring his men from 35k to 50k. OR perhaps 35,000 is their current standing army amongst all of Dorne's bannerman, but it doesn't include recruiting from the smallfolk, as the Lannisters eventually did and the Starks didn't have time to do. If that's true, then Doran didn't lie to Arianne but obfuscated the truth. It doesn't make much sense, but Doran's been known to hide things from his family, and at the time of his revelation in AFFC, he may not have entirely trusted her with his entire plan (which we ourselves don't know yet). As of DwD, he might have given her updated information that the readers are not privy too. Either way, it just doesn't make sense why Doran (who surely instructed Quentyn) would give false information to a potential ally.