Yes, tradecraft dice are based on attribute dice, and can raise when an attribute is increased. Specialized skills are expressed as steps, meaning a ⬆1 rating for a skill raises that tradecraft die type by one step when using that skill.
⬆5 is the maximum number of steps a skill proficiency can raise a die type.
Pages 24 and 100 contain errors. "Improving specialized skills" was written before proficiencies were finalized, and did not get updated before publication. Page 24 should read: As each proficiency is improved, the character sheet should be marked with the appropriate step level for that proficiency. The maximum any proficiency can achieve is ⬆5. The mission point cost of improving a proficiency [...]
Surveillance is mistakenly listed in the rulebook as both a SIGINT (p. 68) and a HUMINT (p. 37) skill. Physical surveillance (tailing another person or vehicle, eavesdropping in public without special equipment, etc.) is a HUMINT skill. SIGINT is only for electronic surveillance, that is, signals intelligence.
No. Each fighting style uses one skill slot. Page 76 states "each fighting style uses one proficiency slot." For clarity's sake, this is changed to "skill slot" in the PDF. When choosing "hand to hand combat" as a skill, the agent must choose one fighting style. Additional fighting styles must be learned using mission points. Fighting styles are an [...]
During their training, ICON agents learn all of the basics of tradecraft, including all the skills and proficiencies listed in the rulebook. "Each field of tradecraft provides the agent a base ability to use any skill related to that field." –Core Rulebook, p. 24 However, agents choose certain areas in which to specialize, which provides them with bonuses when using [...]
On page 85, in "Underwater Combat," the rules refer to a swimming specialized skill. This skill is not included in the list of specialized skills and proficiencies. This was an oversight, and will be corrected in an upcoming rule addendum.