We publish new versions of the library on NuGet:

https://www.nuget.org/packages/BitMiracle.LibTiff.NET/

A copy of the TIFF 6.0 specification is available from Adobe or from the AWare Systems site.

Draft TIFF Technical Note #2 covers problems with the TIFF 6.0 design for embedding JPEG-compressed data in TIFF, and describes an alternative.

You may want to take a look at this supplements to TIFF specification:

TIFF Specification Supplement 1

TIFF Specification Supplement 2

Joris Van Damme maintains TIFF Tag Reference, good source of tag information. It's an overview of known TIFF Tags with properties, short description, and other useful information

You may also find useful to subscribe to The TIFF/LibTiff Mailing List. There are many people with expertise in TIFF willing to share their knowledge. Although LibTiff.Net is not discussed in that list, you may receive answers for you TIFF-related questions there. There is also over ten years of TIFF and LibTiff mailing list activity that you may wish to consult.

The free TIFF Tag Viewer for Windows might also prove useful if you want to check a tiff file properties.