Unlinked headers become linked when last section break in a document is deleted. How can I prevent this?

EDIT/ANSWER: In my specific case, it seems that the easiest way to handle this was to enter the header and footers in the third section. Turn on the "Link to Previous" setting, so that the invisible final section break holding the information for the third section was holding the same information as the section break between the second and third settings. Then, I could delete the section break between the second and third sections. Interestingly, the "Link to Previous" setting automatically turned off. Maybe that info is saved in the prior section?

EDIT: According to this website: https://wordmvp.com/FAQs/Formatting/WorkWithSections.htm the section break between the second and third sections contains the header footer formatting and content information for the second section, so deleting the second section break will delete the second section header and footer information too. Workarounds involve adding additional sections to hold the needed information.

ORIGINAL QUESTION:

I have a document that contains three sections. Each section has different header and footer content and formatting from the header and footer content and formatting in each other section. The first section has different header and footer content and formatting in its first page form the header and footer content and formatting in its remaining pages.

The three sections are separated by section breaks: one between the first and second sections, one between the second and third sections.

The headers and footers in all sections have the "Link to Previous" setting turned off.

The "Different First Page" setting is turned on for the first section. I am not sure if it is turned on for all sections, or if it is possible to turn it on only for one section. It is only needed for the first section.

Sometimes, I need all three sections. However, in this instance, I only need the first two sections, so I want to delete the third section. When I delete the section break between the second and third sections, the headers and footers in the first and second sections become linked, the "Link to Previous" setting automatically turns on for the headers and footers in the second section, and the first section headers and footers are replaced with the formatting and content in the second sections headers and footers.

How can I prevent this behavior? I would like to be able to delete the third section without altering the first and second section header and footer content and settings.

Office 365 running on Windows 10 PC.