Getting an error code when trying to add more conditions/columns to an IF statement

QUERY UPDATED AND CLARIFIED

This is the first time I've worked with more than 1 formula in a cell at a time and also the first time I've tried to work across sheets. I got the template from someone else and I'm having serious trouble modifying it to do what I want. I am working with the following formula in each calendar cell on the second sheet:

=IFERROR(INDEX(Data!$E:$E,SMALL(IF(Data!$F$1:$F$10012<=INDEX(D:D,INT(ROW()/4)*4),IF(Data!$G$1:$G$10012>=INDEX(D:D,INT(ROW()/4)*4),IF(Data!$A$1:$A$10012=$C$1,ROW(Data!$F$1:$F$10012)))),MOD(ROW(),4))),"")

I have a drop down list at the top of the page that allows me to sort by a certain characteristic that lives in column A on the Data sheet. It then populates a calendar with everything that meets those conditions in the specified date range (that part is fine and works great). My problem is that I want to add more conditions for it to meet. Instead of just column A, I need it to look in columns A, B, C, and D and return results that match all of the selected criteria. I already made it so that the dropdown menu can have multiple selections, but the problem is the code in the boxes doesn't know how to look in the other columns to find those selections.

A specific example: I want to select items assigned to Test A, Level 2, in the Test Development department (it would be even better if I could select items assigned to Test A, Levels 1 OR 2, in the test development OR editing departments, but that seems a whole lot more complicated so maybe I'm asking for too much)

I thought it would just be copy and pasting "IF(Data!$A$1:$A$10012=$C$1" multiple times and updating A to be the different columns I want. However, this did not work. I keep getting errors, but it won't tell me why or how to fix it. "Evaluate formula" just adds a bunch of 0's to the formula and doesn't explain anything. I have been reading forums for hours and I am nowhere closer to understanding what is happening.

I am open to adding more drop down lists so each criteria has its own cell at the top if that would make things easier. I just don't really know what I'm doing (obviously)

a couple of variations on a theme that you may be able to adapt.
do not type entries into cells - double click the cell and a data entry form will appear.
if of interest post back on this site.

Ok I think I did this attachment thing right. I have more info for you all because I have been frantically searching the internet for answers. I've come across a few things, but this is the most promising/closest to what I want.

My biggest issue is with the limited sort function. I need to be able to sort multiple things at a time. I need to be able to sort by what exam, what level, and what department. The goal would be for people to be able to sort things such as:
- An editor wants to see all editing deadlines for Level 1
- A publisher wants to see all deadlines related to Levels 1 and 2, but not Level 3
- A manager wants to see all Item Writing Workshops for all levels

Is something like that possible? Is there a way to build off the existing sheet to do that? I added a sheet that shows what I'm imagining as my data points. I don't understand how any of the formulas work and what information I would need to add/change to get to this point.

Bonus: It would be great if I had 12 sheets (1 for each month) instead of 1 that I have to manually change the month on

Edit #2: I've been playing with this and I now have a very specific spot where I'm stuck. Right now the boxes populate using this formula:

=IFERROR(INDEX('What I Have'!$E:$E,SMALL(IF('What I Have'!$F$1:$F$10012<=INDEX(D:D,INT(ROW()/4)*4),IF('What I Have'!$G$1:$G$10012>=INDEX(D:D,INT(ROW()/4)*4),IF('What I Have'!$A$1:$A$10012=$C$1,ROW('What I Have'!$F$1:$F$10012)))),MOD(ROW(),4))),"")

It currently tries to match what is in cell C1 with anything in column A on the other sheet. What I need to do is isolate which part of this formula is doing that and duplicate it for other columns. E.g. In D1 I would have drop downs for column 2, E1 would have dropdowns for column C. Then it would be able to populate the cells with all things that meet those 3 criteria.

I made a post a few hours ago that I think was just too big/vague. I needed more answers/work than 1 person should have to provide for free. Since then I have been working furiously on this and have found a spreadsheet that functions in somewhat the way I want. I now have a very specific spot where I'm stuck. Right now the boxes on the event sheet populate using this formula:

=IFERROR(INDEX(Data!$E:$E,SMALL(IF(Data!$F$1:$F$10012<=INDEX(D:D,INT(ROW()/4)*4),IF(Data!$G$1:$G$10012>=INDEX(D:D,INT(ROW()/4)*4),IF(Data!$A$1:$A$10012=$C$1,ROW(Data!$F$1:$F$10012)))),MOD(ROW(),4))),"")

There is currently a dropdown menu in C1 that aligns with items in column A and the above formula is what matches the content and populates a cell. What I need to do is isolate which part of this formula is doing that and duplicate it for other columns. In D1 I would have drop downs for column B, E1 would have dropdowns for column C, etc...Then when I make my choices it would populate the cells with all things that meet those all of those criteria. It would also be great if it was checkboxes like a pivot table instead of a single selection (e.g. instead of being limited to only Level 1 or Level 2 items, I could see both together).

hopefully @PeteUK may see this post and help you - he has far more experience than I with calendars embeded with formula.
I tend to steer away from on sheet formula and take the path of VBA code solutions.

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