There are two separable issues: How Lightroom reads metadata fields from photos, and how Windows Explorer writes metadata fields. Unfortunately, I don't think there is a single authoritative document describing either issue. The industry has made a legacy mess of metadata, and very few programs attempt to do a high-quality job.
Lightroom does a reasonable job of following the industry standard published by the Metadata Working Group. That standard unifies the three main mechanisms in which metadata is stored in JPEGs and other file formats: EXIF, IPTC, and XMP. Many fields have defined slots in each of those three mechanisms. For example, the capture time can be stored in EXIF:DateTimeOriginal, IPTC:DateCreated and IPTC:TimeCreated, and in XMP:DateCreated. The MWG standard specifies how applications should read and write those multiple fields.
For a couple of the most commonly used fields, LR uses its own names: "caption" (for EXIF:ImageDescription, IPTC:Caption-Abstract, XMP:Description); "capture date" (see above); "title" (IPTC:ObjectName, XMP:Title). But for the rest of the fields, LR generally uses the same name as defined in the EXIF or IPTC standards -- these are the names displayed in the EXIF and IPTC presets in the Metadata panel in the right column of the Library.
There is one dark corner where LR has made a mess: photos missing capture date/time (e.g. scans or very old digital photos). Some parts of LR will use the file's last-modified time, others the file's create-time (as set by the Windows or Mac operating systems). This yields very confusing, inconsistent results that is easily corrected by using the Metadata > Edit Capture Time command.
Regarding Windows File Explorer, since Windows 7, Microsoft has actually done a better-than-average job of following the industry standards (a little better than Mac Finder), but that's a pretty low bar, especially considering that there are multiple standards to choose from, and File Explorer has its own share of quirks. It's been a while since I looked at File Explorer in depth, but I recall that it (like virtually every other application, including LR) uses names for the fields that don't necessarily correspond closely to the names assigned by the standards. For example, File Explorer's "Title" gets mapped to EXIF:ImageDescription, EXIF:Title, EXIF:Description, and IPTC:Caption-Abstract.
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If you really care about getting your 20-years-worth of photos loaded correctly into LR (and I think you do), then your best best is to download the free "exiftool" and learn how to use it. It's the most authoritative tool bar none for examining and manipulating metadata. To see where fields are getting stored, I use this command line:
exiftool -a -G file.jpg
I think there are GUI versions of Exiftool available, but in the past, they didn't keep up with the core tool, and after a while, I found they just in the way.
Then with a little trial and error you can see exactly where the fields you've stored with File Explorer are getting stored and whether LR is reading them correctly.