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For over 20 years he has led seminars and courses on relationships and communication, and he has appeared on television shows.
why don't we use continuous because it is up to now? Is it because 20 years is a long time and we can't use the continuous form or is it because he did not always lead seminars, may be two years could pass between seminars
As constructed the sentence is awkward. As you noticed, if we assume the subject is still leading his seminars, then the present perfect continuous would have been better (or at least more accurate):
He has been leading seminars and courses ...
Meanwhile, since his appearances on television are not necessarily ongoing, the present perfect is probably more descriptive.
He has (also) appeared on television shows ...
The challenge here is style, not grammar. As with writing in any language, there is good style and not-so-good style. In English, when making a "list" of things (like accomplishments) it's considered good style to use the same structure for all the elements of the list. For example:
Her hobbies include reading cookbooks filled with recipes she'll never make, writing novels she never intends to finish, and watching travel shows about places she knows she'll never visit.
My guess is that the author is trying to follow the rules of good style, by making both verbs in the present perfect, but at the sacrifice of accuracy. This is not grammatically wrong, just inelegant. But sometimes you have to make choices.
