The "index" function has two syntaxes. I implemented the syntax 1. The "cell" function allows retrieving several types information. I implemented the type of "contents". It's able to solve the formula problems currently.
I've finally managed to test out v1.7.4.2. Its working better, but I've run into a minor issue.
=+'Input sheet'!D4
This formula works fine when the value in D4 is a numeric value, but if it is a string, I get a "Wrong Number Value" error. In excel, it returns the string value.
I didn't run into any other formula errors, and I'm crossing my fingers that the client doesn't throw us any more files with other formulas in them.