You need a more specific expression. Try grep " OK$"
or grep "[0-9]* OK"
. You want to choose a pattern that matches what you want, but won't match what you don't want. That pattern will depend upon what your whole file contents might look like.
You can also do: grep -w "OK"
which will only match a whole word "OK", such as "1 OK" but won't match "1OK" or "OKFINE".
$ cat test.txt | grep -w "OK"
1 OK
2 OK
4 OK
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