Thanks Sunny;
you are right - I did not include enough examples/possibilities in my post.
Nonetheless, I used your formula to tweak my original formula to make it work.
For those interested, my original target string was based on "=CELL("filename", A3)", which would produce the following
[TABLE="width: 888"]
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[TD="class: xl49476, width: 888"]Q:\Corporate Financial\Planning and Performance Measurement\05 Forecasting\Forecast Model\2018 01\[Expenses, CFF.xlsx]Misc
"=MID(B$3, FIND("\[", B$3)-7, 7)" will extract the date.
This does not work if the "\2018 01\" is anywhere else in the string.
Also, I did not include (in the original post) a potential "\2018\" within this string [my bad!].
My final solution:
New string: "=SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(CELL("filename", A3), "\2018", ""), "\2019", ""), "\2020", "")"
Date Extract: "=MID(B$3, SEARCH("20", B$3), 7)"
[/TD]
[/TR]
</tbody>[/TABLE]
The new string formula is not the most eloquent formula I've written, but the sheet layout limits my options.
It is likely adequate for my purposes (and in fact, I included enough substitutions for 6 years just to be sure!)
Again, thanks for your input, Sunny!