Adobe has never offered a font or font family with the simple name “Garamond.” Adobe has offered Adobe Garamond (Type 1 and subsequently OpenType CFF formats) and Garamond Premier Pro (OpenType CFF format) families, both Adobe designs, as well as ITC Garamond, Garamond 3, and Stempel Garamond licensed from other foundries.
My initial assumption was that the “Garamond” that you are most likely using is the Garamond family installed by Microsoft Office, licensed by Microsoft from Monotype. Ironically, this font family only has regular, italic, and bold faces. There is no bold italic face with that particular Garamond family. And apparently, for some reason, your Windows configuration refuses to “synthesize” a bold italic faux style for Garamond by obliquing Garamond Bold. (I am successful in doing this on my systems - I don't know why it doesn't work on yours).
However, you mention uninstalling and reinstalling .pfb and .pfm files. That would be indicative of a Type 1 version of a Garamond font family. What I did find what that the old Type 1 ITC Garamond fonts licensed by Adobe indeed had a Windows application menu name of Garamond. That may be what you have been using.
If that's the case, the cause of the problem is unfortunately very simple. Microsoft no long supports any Type 1 fonts (i.e., the fonts with .pfb and .pfm files) for Microsoft Office under Windows starting with Office 2013, although the Type 1 font names may appear on the font lists. What is probably happening is that Word is using the Monotype TrueType version of the regular, italic, and bold faces of Garamond but then has no direct substitute for the Type 1 bold italic face of Garamond, thus using Arial Bold Italic. That is consistent with the sample you display. (The Garamond in your sample does not look like ITC Garamond!)
Since Adobe applications continue to fully support the old Type 1 fonts (although we no longer sell licenses for them), you don't see this problem in any Adobe application.
For better or worse, there is nothing Adobe can do to assist you with this since the problem is neither caused by any Adobe software nor can it be fixed by anything from Adobe. And Microsoft has no intention of supporting Type 1 fonts going into the future. They do support TrueType, OpenType TrueType, and OpenType CFF (Type 1 outlines) fonts now!
What are your alternatives? You could license TrueType, OpenType, or OpenType CFF versions of some version of Garamond from Adobe or some other vendor after carefully matching what you currently have in terms of style with Garamond fonts available. (Note that there are dramatic differences between the available Garamond typeface families even though they all have “Garamond” in their names!) You will probably need to modify your branding documents and document libraries to reflect the new font name(s).
Yes, this is a royal pain in the tuchas, but it was Microsoft's choice to stop supporting Type 1 fonts. 
Let us know if there is anything we can further assist with in terms of this issue.
- Dov