How to explain a missing grade card in unofficial transcript for online graduate application? I'm an international pre-final year undergraduate student. My undergraduate degree consists of 8 semesters and I'm currently in the 6th semester. I'm hoping to apply to US mathematics graduate schools this Nov-Dec, for Fall 2021. I missed a final exam in the 4th semester due to medical reasons and was supposed to re-appear for it in May 2020. However, now that re-test will probably be scheduled in December due to COVID and I won't get the results before the US application deadlines this year.  Moreover, I was not issued any grade card for that 4th semester. 

Now several US math graduate programs say that they only require unofficial transcripts in the online application and that hard copy official transcripts can be submitted later. So would it make sense to apply anyway with only my 1st, 2nd, 3rd, 5th, and 6th semester grade cards, and with the 4th semester grade card missing? Would I have to explain that one missing grade card in the online application? If yes, how? Say, would a letter from my head of department, explaining the situation be helpful? I will hopefully get my 4th semester results by March 2021 though, so I think I will later be able to send the official hard copy transcripts in time, in case I get an admit.
If you don't apply, you don't get in. Simple. If you do, then there may be some difficulties, but many of them can probably be overcome in the eyes of most institutions. Given the current pandemic, people are going to have to be flexible. 

I'd suggest that you have someone, maybe the department head, provide an unofficial listing of your courses and grades for that semester. Perhaps they are allowed access to grades, but they can also contact your professors to verify the grades if necessary. Explaining the grading process at your university would also be useful in such a note. 

A note from you explaining the situation might be helpful, since the reason was medical and the delay is well explained. 

I can't guarantee that anyone would necessarily accept this, but suspect that most will, especially since they only need official transcripts later. 

But, again, you have little (almost nothing) to lose by making a good faith attempt and putting together the best record you can for admission. People will be looking for evidence that you will succeed. Provide that.