Do specialists and doctors share information?

@bryanta Why don't they share? Here comes that dreaded answer - It depends.
In a perfect world, all of our specialists would be linked together and see out entire medical record. BUT...Doctors and their staffs are insanely busy just trying to manage their own piece of the puzzle. Unless a report from another specialist is critical to what you are seeing them for, there is no time to study a patient's full record.
Systems developed separately over time that do not necessarily "talk" to one another. Even one "Epic" system and another may not link.
Privacy regulations limit what providers can see about you without specific permissions.

What can we do as proactive consumers of medical services?
If one doctor referred you to another, in or out of network, make sure the new doc shares their findings with the first one. You may have to sign a release, provide a fax number, etc.
If you regularly see doctors in different networks, make sure they have access to each others' records. This may require working with their support staffs to set up.
If all else fails, carry a clear, printed, scannable copy of any relevant test results or visit/diagnostic reports to your appointments. This is a last choice, because the documents scan as .pdf files, and are not actually integrated into your records, but saved as "notes."

As for unanswered questions sent through the portal, whether Epic or something else, if I don't get a response, I follow up after 3 days with a phone message requesting an answer. It hasn't failed yet.

Since you have a complex medical history, have you considered creating a two-page (no longer) summary of your diagnoses, from most to least critical, with date of diagnosis, doctor's name & contact info, current treatment? You may have to omit very old or minor issues to get to 2 pages. For example, I would omit treatment for plantar fasciitis (now resolved), omit successful sinuplasty 25 years ago, summarize all my hip replacement/revision surgeries to one entry and my vision issues to another.

They should but it is time consuming. I waited 6 months to see a specialist at UCLA. Then I waited two hours in the room while the new fellow read my fat chart. He came in first, and was marvelous. He had good ideas and great suggestions. Everyone was laughing that new fellow had read the entire chart. The presiding resident came in and dismissed the fellow's every thought. She treated everything with MAOIs. She was useless for me. She did give me a pack of otc peppermints, which I took so I could tell my Mom a funnier story.
Some of these docs are brilliant but they don't have the time.
It is important to remember that they don't remember even what you told them in the last appointment.

@sueinmn I hesitated before I paid the concierge doctor for another year of service because “Who would take the time to read my file?”
What medical records should I keep handy? I’ve been relying on Patient Portals. Copies of lab results Procedures? MRI’s? I know what tax return info to save but am clueless when it comes to medical records.
Your post was thorough. If I make a change to a new PCP, would it be best to provide this doctor with additional records?