High Functioning Aspies tend to be undiagnosed because their condition is usually masked by an above-average intelligence. In fact, many have a high IQ and are over represented in Science, Technology, Engineering and Maths (Cambridge University study).
Intelligence is comprised of both fluid intelligence and crystallised intelligence. Studies suggest that Aspies have superior abstract reasoning ability or higher general fluid intelligence. They also tend to acquire more crystallised intelligence knowledge and at faster rates than NeuroTypical people. This process of acquiring factual knowledge is sometimes called Cognitive Investment
Fluid intelligence is the capacity to think logically and solve problems in novel situations, independent of acquired knowledge. It includes such abilities as pattern recognition, abstract reasoning and problem-solving. It It is the ability to analyse novel problems, identify patterns and relationships that underpin these problems and the extrapolation of these using logic. It is necessary for all logical problem solving, especially scientific, mathematical and technical problem solving. Fluid reasoning includes inductive reasoning and deductive reasoning, and is one of the Aspie's strengths to an employer.
Crystallised intelligence, on the other hand, is the ability to use skills, knowledge, and experience. It is indicated by a person's depth and breadth of general knowledge, vocabulary, and the ability to reason using words and numbers. However, this is not the same as memory or knowledge, but it does rely on accessing information from long-term memory. Crystallised intelligence is one’s lifetime or intellectual achievement, as demonstrated largely through one's vocabulary and general knowledge. This improves somewhat with age, as experiences tend to expand one's knowledge.