Yes, for part A. No one is required to check for the use of patent or check on the methods they employ, if they unknowingly do it and there is no patent protection for a manufactured product or a patent protection for a method they employ in a place where no protection has ever been.
Unclear question, for part B. If the patent covers the use of the intellectual property being employed under the specifics at hand and the patent is infringed by another, then it is enforceable in a court of competent jurisdiction and is therefore considered "in force," otherwise the answer is no definitely not.
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Whether the party in question who is infringing by some action the intellectual property rights of another is a "regigistered US Company" is immaterial to the real question of infringement as long as the "other party" is a real entity defined by law to be within the jurisdiction of the court of competency who renders the decision and may announce a judgement for which the "other party" can legally respond.