To Be … or not to be … Pages?

I am helping an organization convert a well-established HTML-based site over to WP. Most of the issues are handled, but there’s one that I have been giving serious consideration to, but want to get some feedback from others before proceeding.

For directories currently in the HTML site, there are the static homepages (the old index.html pages). In moving to WP, the organization is working to preserve the same links, when possible. In fact, I’ve been working — because of the organization’s policies against linkrot — and going out of my way to preserve the links.

That said, let’s say I have a page:

https://YourDomain.com/DirectoryName/

Because of the server setup, we’ve never given anyone the actual file name or extention for the homepages in the directories. That’s not a biggie, as we can resolve that by using a category to get them to that page. A WP Page could even work, if needed.

Enter the problem.

There have several very popular pages that are well-known, and some that have been published in books and manuals. They are also in most of the organization’s printed materials, and reprinting everything right now means that hundreds of thousands of copies are dumped in the recycling bin because of URLs, so that isn’t an option.

The pages giving the biggest problems are those that are child pages in the directory, making their path, in the HTML site, something like:

https://YourDomain.com/DirectoryName/PageName1.htm
and
https://YourDomain.com/DirectoryName/PageName2.htm

Here is where I am trying to arrive at the best solution. I want to use WP to deliver them to:

https://YourDomain.com/DirectoryName/PageName1
and
https://YourDomain.com/DirectoryName/PageName2

Faking the “.htm” extension isn’t an issue, as that’s easy enough to pull off. I am wanting to get others’ thought and feedback on the best way to keep the page names, as described in the paragraph immediately above, so the links are still valid.

Tossing in redirects could work, but the organization would rather not do that for a variety of reasons. So, does anyone have ideas or solutions to create make:

https://YourDomain.com/DirectoryName/PageName1
and
https://YourDomain.com/DirectoryName/PageName2

appear, (forget the .htm part — that’s solved)

One issue is:
using categories as the “directory name” won’t solve it entirely, as the categories are being used such as:

Program 1
Program 2
Issue 1
Issue 2
Issue 3
News Item 1
News Item 2

Since the directory path name is Program 1, but also falls into Issue 2, Issue 2, and News Item 2, categories alone will not work in faking the HTML directory paths.

TIA!