Google Script / Javascript includes() function not matching when expected with valid input

I'm struggling to figure out why the Javascript includes() function I'm using here isn't matching and returning true. The code is used in a Google Script on a Google Sheet to populate some cell values. Here's the relevant code from the full script:

const currentYear = getCurrentYear();

//Get current year from active sheet name
function getCurrentYear(){

  year = sheetName.slice(-7, -2);
  return year; //returns "2020"

}

//Return Current Control File ID
function getCurrentControlFileId(){
  
  const controlFolder = DriveApp.getFolderById(controlFolderId);
  const controlFiles = controlFolder.getFiles();
  
  while (controlFiles.hasNext()){
    let controlFile = controlFiles.next();
    let currentControlFileName = controlFile.getName(); // Evaluates to "CONTROL 2020"
    let searchString = `${currentYear}`; // Evaluates to "2020"
    //Have also tried:
    //let searchString = currentYear; 
    
    if (currentControlFileName.includes(searchString)){
      let controlFileId = controlFile.getId();
      return controlFileId;
    }
  }
  
}

controlFile.getName().includes(searchString) returns false even though controlFile.getName() value is "CONTROL 2020" and searchString value is "2020". Both are strings. If I manually enter "2020" into the if statement conditions like this:

controlFile.getName().includes("2020") it returns true and works as expected, returning the ID string. I've also tried wrapping currentYear and controlFile.getName() in String() but it still returns false. I really can't see what the problem is here, would appreciate some help.