You are using quotation marks for numbers - this tells Excel to treat it as texts. As such, "9" and "12" has different sizes than the numeric 9 and 12. That is "12" is actually less than "9". I would recommend working with actual numeric figures instead, as you've down for numbers between 1 and 4. Removing all quotation marks around the numbers should resolve the issue.
Additionally, you are comparing "Lvl 17" and "Lvl 20" - this is inconsistent with the other comparison type where you only look at the numbers and do not include the text Lvl. Potential error here.
Also, the final IF function you have (Lvl 17 and Lvl 20) does not have a value_if_false component, and will result in FALSE if the number in K4 does not meet any of the requirements.
Lastly, looking at your formula, it seems like it can be simplified to a LOOKUP, i.e.
Formula:
=LOOKUP($K$4, {1,5,9,13,17}, {"+2", "+3", "+4", "+5", "+6"})
Bookmarks