Passive constructions in the present simple tense can refer to a particular time or situation:
I am bored by him. (Can mean "at the moment".)
She is alleged to be cheating on her husband.
And CNN is now calling it: Barack Obama is elected president this historic day.
Ten minutes into the film, the main character is hit by a train.
It is more common to see such constructions used to describe things that happen regularly or are general truths:
They are awakened every morning by the garbage truck.
Tomatoes are picked while still green and quite firm.
There is often confusion between passive constructions containing a verb in past participle form, and a statement where such words function as adjectives. We sometimes need to rely on context to determine which is the case. Sometimes it is impossible to make such a determination from the available information, or the line is too fuzzy to be drawn with certainty.
Active construction (subject + verb + adjective [complement]):
The store is closed. We arrived too late.
Passive construction:
The store is normally closed by the assistant manager.
Should I use the present continuous with a passive form to mean that the status (being insured) is currently permanent, but will change later?
To say that something is insured for a year is unclear to begin with. Does that mean that it was originally insured for a period of one year, and it does not matter when that happened and when it will expire? I think that in almost any context, we would want to communicate when the term began and/or when it will end. Also, the wording Professional liability of a specialist is not idiomatic in most contexts.
If we want to say something like
The specialist's professional liability is insured with ABC Insurance Co., for a term of one year.
We could not use the present continuous tense because that would suggest that the activity of being/becoming insured is occurring as a process at the time of speaking.
For the second question, a correct version of that utterance is
In the report, the supervisor particularly notes that a number of serious errors have not been corrected by a worker, despite previous warnings by management.
We would usually avoid using "are not being corrected" because that could mean that an act of correcting is not occurring at the moment. However, it could also mean that the lack of correction is persisting over a period of time. Most good writers would avoid the present continuous without making clear which of those senses they wanted to denote.
Your initial examples are not as unambiguous as you think, and that is probably leading to later confusion. The continuous effect is not as baked in as you make it out to be.
"I'm having dinner at 2:00" actually sounds like dinner is scheduled to start at 2:00.
"I was having dinner at 2:00" could it was ongoing in the past at 2:00, or the 'was' could be subjunctive introducing doubt, meaning plans were changed ("I was having dinner at 2:00, but I missed the bus so we ate at 3:00"). Or even just that plans have been cast into doubt (eg "I was going to Toshi Station to pick up some power converters" -L. Skywalker)
"I will be having dinner at 2:00" could be grammatically be either ongoing or a scheduled start.
Your simple tense examples mostly work, although "I have my dinner at 2:00" sounds like it means "I have dinner at 2:00 every day" more normal usage for a specific upcoming event is "I will have dinner at 2:00"
Anyway, the main point is that the 'ongoing nature' isn't as firm a rule as you are looking for. So that's why there's nothing broken about "I'm having dinner at 2:00 tomorrow" with 2:00 being the start time.
Best Answer
The difference is "forever" or "indefinitely" versus "for some defined period of time".
Like, "Newton's Laws describe the motion of objects." I expect those laws to be true forever.
Sure, in practice, most things don't really last "forever". But some things will continue for an undefined period of time. There is no plan or expectation that they will change.
So for example, "My school teaches French and Spanish" versus "I am studying French and Spanish". In the first case, the school teaches these subjects and it will continue to teach them indefinitely. In the second case, I expect to graduate within a few years and so I will no longer be studying these languages.
Of course one could say that the school won't remain in operation literally forever. Sooner or later the school will be closed for one reason or another. Or even if it stays in operation, it may change what classes it teaches. But the point is that we expect it to keep teaching these same classes indefinitely.
Yes, there are debatable cases. Like, "Fred lives in Chicago." There is no guarantee that Fred won't move to another city some day. Even if he doesn't, he's going to die sooner or later so will no longer "live" anywhere. But if Fred has no plans to move any time soon, we'd use the simple present. If he's just living in Chicago temporarily until he gets a job or graduates from school or some other expected event, then we'd say, "Fred is living in Chicago."
So it's not a matter of 1 years versus 2 years or any specific numbers. It's more like, There's no reason to expect a change versus There is a reason to expect a change. Whether the "reason" here is the laws of nature, a human being's intentions, or something else, depends on context. Likewise, in context "indefinitely" could mean "for at least a few hours" or "for thousands of years".